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As filed with the Securities and Exchange Commission on October 10, 2002

Registration No. 333-            

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM S-3
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

Aon CORPORATION
(Exact name of registrant as specified in its charter)

Delaware 36-3051915
(State of incorporation) (I.R.S. Employer Identification No.)

200 East Randolph Street
Chicago, Illinois 60601
(312) 381-1000
(Address, including zip code, and telephone number, including
area code, of registrant's principal executive offices)

Raymond I. Skilling, Executive Vice President and Chief Counsel
Aon Corporation
200 East Randolph Street
Chicago, Illinois 60601
(312) 381-1000
(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copy of communications to:

James T. Seery
Piper Rudnick LLP
1251 Avenue of the Americas
New York, New York 10020
(212) 835-6000

Approximate date of commencement of proposed sale to the public:
From time to time after this Registration Statement becomes effective.

        If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box. o

        If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box. ý

        If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

        If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. o

        If delivery of the prospectus is expected to be made pursuant to Rule 434, please check the following box. o

CALCULATION OF REGISTRATION FEE

Title of Each Class of Securities to be Registered
   Amount to be Registered
   Proposed Maximum Offering Price Per Unit
   Proposed Maximum Aggregate Offering Price
   Amount of Registration Fee
Common stock, par value $1.00 per share   700,000(1)   $18.12(2)   $12,684,000(2)   $1,167(2)
(1)
This amount does not include up to 3,864,824 shares of unsold common stock covered by Registration Statement No. 333-49300.
(2)
The fee was calculated pursuant to Rule 457(c) under the Securities Act of 1933 and was based on the average of the high and low prices of the Common Stock on the New York Stock Exchange on October 7, 2002. Pursuant to Rule 429(b), a filing fee of $32,905 was paid in connection with the filing of Registration Statement No. 333-49300.

        Pursuant to Rule 429 under the Securities Act of 1933, the Prospectus herein is a combined Prospectus and also relates to up to 3,864,824 shares of unsold common stock covered by Registration Statement No. 333-49300 previously filed with the Commission on Form S-3 and declared effective November 15, 2000. This Registration Statement also constitutes Post-Effective Amendment No. 1 to Registration Statement No. 333-49300.

        The registrant hereby amends this registration statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this registration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the registration statement shall become effective on such date as the Commission, acting pursuant to said Section 8(a), may determine.

Subject To Completion, Dated October 9, 2002

The information in this prospectus is not complete and may be changed. The selling shareholders may not sell these securities until the registration statement filed with the Securities and Exchange Commission is effective. This prospectus is not an offer to sell these securities and it is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

Prospectus

Aon CORPORATION

4,564,824 SHARES

COMMON STOCK

        This prospectus relates to 4,564,824 shares of common stock of Aon Corporation. The stockholders selling the shares in this offering have the right to determine both the number of shares they will offer and the time or times when they will offer the shares. They may sell the shares at the market price at the time of sale or at such other prices as they may negotiate. All of the shares covered by this prospectus were originally issued by Aon in connection with the acquisition of ASA Acquisition Corp.

        The selling stockholders will receive all of the net proceeds from the sale of the shares offered hereby and will pay all underwriting discounts and selling commissions, if any, applicable to the sale of the shares.

        The common stock is traded on the New York Stock Exchange under the symbol "AOC."

        Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or determined if this prospectus is truthful or complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is                , 2002.


TABLE OF CONTENTS

 
   Page
Where You Can Find More Information   1

Special Note on Forward-Looking Statements
 
2

The Company
 
3

The Offering
 
3

Use of Proceeds
 
4

Selling Stockholders
 
4

Plan of Distribution
 
16

Legal Matters
 
17

Experts
 
17


WHERE YOU CAN FIND MORE INFORMATION

        We file annual, quarterly and special reports, proxy statements, and other information with the Securities and Exchange Commission. You may read and copy any document we file with the SEC at the SEC's Public Reference Room at 450 Fifth Street, N.W., Washington, D.C. 20549 or at the SEC's regional offices located at Citicorp Center, 500 West Madison Street, Suite 1400, Chicago, Illinois 60661-2511 and 233 Broadway, New York, New York 10005. You may obtain further information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. Our SEC filings are also available to the public over the Internet at the SEC's Web site at http://www.sec.gov. In addition, you may inspect our SEC filings at the offices of the New York Stock Exchange, 20 Broad Street, New York, New York 10005, the Chicago Stock Exchange, 440 South LaSalle Street, Chicago, Illinois 60605 and the London Stock Exchange, Old Broad Street, London, England EC2N 1HP. You may find additional information about Aon Corporation and its subsidiaries at our Web site at http://www.aon.com. The information on our web site is not a part of this prospectus.

        The SEC allows us to "incorporate by reference" into this prospectus the information we file with the SEC, which means that we can disclose important information to you by referring you to those documents. Any information referenced this way is considered to be part of this prospectus, and any information that we file later with the SEC will automatically update and supersede this information. We incorporate by reference the documents listed below and any future filings we make with the SEC under Sections 13(a), 13(c), 14 or 15(d) of the Securities Exchange Act of 1934 until all of the securities covered by this prospectus are sold by the selling stockholders.

        This prospectus is a part of a registration statement we have filed with the SEC relating to the securities. As permitted by SEC rules, this prospectus does not contain all of the information included in the registration statement and the accompanying exhibits and schedules we file with the SEC. You may refer to the registration statement and the exhibits and schedules for more information about us and our securities. The registration statement and exhibits and schedules are also available at the SEC's Public Reference Room or through its Web site.

1


        You may obtain a copy of these filings, at no cost, by writing to or telephoning us at the following address:

Aon Corporation
200 East Randolph Drive
Chicago, Illinois 60601
Telephone (312) 381-1000
Attention: Corporate Secretary

        You should rely only on the information incorporated by reference or provided in this prospectus. We have not authorized anyone else to provide you with different information. You should not assume that the information in this prospectus is accurate as of any date other than the date on the cover of the applicable document. We are not making an offer of the securities in any state where the offer or sale is not permitted.


SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS

        This prospectus and the documents incorporated or deemed to be incorporated by reference herein contain statements concerning our future results and performance and other matters that are "forward-looking" statements within the meaning of Section 27A of the Securities Act and Section 21E of the Securities Exchange Act of 1934. The words "anticipates," "believes," "estimates," "expects," "plans," "intends" and similar expressions are intended, but are not the exclusive means, to identify these forward-looking statements. These forward-looking statements are subject to certain risks and uncertainties that could cause actual results to differ materially from historical or anticipated results, depending on a variety of factors. Potential factors that could impact results include:

        In light of these risks, uncertainties and assumptions, the forward-looking events discussed in this prospectus or documents incorporated or deemed to be incorporated by reference herein might not occur. We will not update forward-looking statements even though our situation may change in the future.

2



THE COMPANY

        We are a holding company whose operating subsidiaries carry on business in three distinct operating segments: (i) insurance brokerage and other services, (ii) consulting and (iii) insurance underwriting.

        Our insurance brokerage and other services segment consists principally of our retail, reinsurance and wholesale brokerage, as well as related insurance services, including claims services, underwriting management, captive insurance company management services and premium financing. These services are provided by subsidiaries of Aon Group, Inc., and certain of our other indirect subsidiaries, including Aon Risk Services Companies, Inc.; Aon Holdings International bv; Aon Services Group, Inc.; Aon Re Worldwide, Inc.; Aon Limited (U.K.); Cananwill, Inc.; and Premier Auto Finance, Inc.

        Our consulting segment provides a full range of human capital management services utilizing five practices: employee benefits, compensation, management consulting, outsourcing and communications. These services are provided primarily by subsidiaries and affiliates of Aon Consulting Worldwide, Inc., which is also a subsidiary of Aon Group.

        Our insurance underwriting segment is comprised of supplemental accident and health and life insurance and extended warranty and casualty insurance products and services. Combined Insurance Company of America engages in the marketing and underwriting of accident and health and life insurance products. Combined Specialty Insurance Company (formerly known as Virginia Surety Company, Inc.) and London General Insurance Company Limited offer extended warranty and casualty insurance products and services.

        We have 550 offices in over 125 countries and sovereignties and nearly 53,000 professionals and employees who serve millions of clients, policyholders and warrantyholders.

        The mailing address of our principal executive offices is 200 East Randolph Street, Chicago, Illinois 60601, and the telephone number of our principal executive offices is (312) 381-1000.


THE OFFERING

Common stock offered by selling stockholders   4,564,824 shares
Common stock outstanding as of October 7, 2002   295,365,361 shares
New York Stock Exchange Symbol   AOC
Use of proceeds   We will not receive any proceeds from the sale of the common stock being offered by this prospectus.

        The purpose of this offering is to register the resale of the shares of common stock received by the selling stockholders, including shares of common stock issued to certain stockholders as contingent merger consideration, in connection with our acquisition of ASA Acquisition Corp., a New Jersey corporation. On October 2, 2000, Aon acquired all of the issued and outstanding common stock of ASA, through the merger of a wholly-owned subsidiary of Aon, with and into ASA. Pursuant to the terms of the merger agreement, Aon is obligated to issue contingent merger consideration in the form of common stock to certain eligible stockholders. In connection with the merger, Aon entered into a registration rights agreement, which requires Aon to use its best efforts to file, and cause to be declared effective, a registration statement for the shares issued in the merger, including those shares issued as contingent merger consideration, and to keep the registration statement continuously effective until the earlier of

3


USE OF PROCEEDS

        The selling stockholders will receive all of the proceeds from any sale of our common stock offered under this prospectus. We will not receive any proceeds from the sale of the common stock offered under this prospectus.


SELLING STOCKHOLDERS

        The following table sets forth:

        (1)  the name of each selling stockholder,

        (2)  the nature of any position, office or other material relationship which each such selling stockholder has had with us or any of our affiliates within the last three years,

        (3)  the number of shares of common stock owned by each such selling stockholder prior to the offering,

        (4)  the number of shares of common stock owned offered for each such selling stockholder's account, and

        (5)  the number of shares of common stock owned by each such selling stockholder after completion of the offering.

        All of the selling stockholders were employees or representatives of ASA at or prior to the date of the merger of ASA with and into a subsidiary of Aon. A substantial majority of the selling stockholders are employed by subsidiaries of Aon. No selling stockholders will own one percent or more of our common stock following the offering.

4


Selling Stockholder
   Number of
Shares Owned
Prior to Offering
   Number of
Shares to
be Sold
   Number of
Shares Owned
After Offering
Ramanand Achanta   329   329   0
Darius Adams   12   12   0
Terry Adamson   2,344   2,344   0
John Albrecht   31   31   0
Ian Alex   1,109   1,109   0
Vicken Alexanian   289   289   0
Anthony Allen   28   28   0
Michael J. Allen   19   19   0
Sandra Allende   12   12   0
David Alpert   888   888   0
Ruth Anderman-Lanza   477   477   0
Thomas P. Anderson   1,830   1,830   0
Irlande Andre-Johnson   31   31   0
Kristie L. Andresen   976   976   0
Ted Mark Andrews   13,860   13,860   0
Michael Andrews-Kulis   19   19   0
Robert Angelica   17   17   0
Mary Ann Arlt   25,100   25,100   0
Kevin R. Armant   6,025   6,025   0
Paulette Askew   68   68   0
Michelle Atchley   342   342   0
Bradley J. Au   4,436   4,436   0
Aleksander Ayerov   831   831   0
Suresh Babu   56   56   0
Thomas A. Bainbridge   111   111   0
Thomas G. Bainbridge   54,726   54,726   0
Cecilia Baita-Elhattab   11   11   0
John F. Balaban   4,678   4,678   0
Sofia Balios   477   477   0
Ricc Ballard   162   162   0
Brendon M. Banks   102   102   0
Laurie L. Banwart   169   169   0
Randall Barnett   1,441   1,441   0
Kalyan K. Basu   104,991   104,991   0
Bridget C. Bauer   68   68   0
Deborah Beatty   12   12   0
Art Beauchamp   1,405   1,405   0
Franklin B. Becker   194,503   194,503   0
Michele M. Becker   5,637   5,637   0
Michelle L. Belcaro   28   28   0
Janet M. Bellis   8   8   0
June E. Benkiel   68   68   0
Nancy T. Bertram   554   554   0
Nimisha V. Bhatt   477   477   0
Ame R.T. Biggart   1,845   1,845   0
Amy Bigge   318   318   0
Gretchen Bilhardt   1,830   1,830   0
Leonard R. Billa   340   340   0
Ann Marie Black   100   100   0
Jennifer L. Black   318   318   0

5

Lori A. Black   64   64   0
Charles Blanchard   162   162   0
Jay E. Blumenreich   2,218   2,218   0
Luke Bodenstein   318   318   0
Carol A. Boettger   442   442   0
Christopher M. Bone   150,230   150,230   0
Larry Booth   68   68   0
Scott Borchers   437   437   0
Lewis Borgenicht   31,919   31,919   0
Lesley Bourne   68   68   0
Deborah Bowers   97   97   0
Stephen Boyar   8,892   8,892   0
Jo-Anne Bragg   1,386   1,386   0
Ben S. Brandon   457   457   0
Joseph Brechka   1,386   1,386   0
John Breitwieser   1,663   1,663   0
Mary Denise Bruton   1,275   1,275   0
Stephen Bryson   1,386   1,386   0
Mark Brzostowski   9,980   9,980   0
James F. Buchanan   554   554   0
Jeffrey Buchman   3,603   3,603   0
Ronald W. Buesser   1,663   1,663   0
Michael Bullard   1,595   1,595   0
Carol D. Bunton   887   887   0
Victor Buonopane   2,221   2,221   0
Roger L. Burke   68   68   0
Thomas J. Burmester   128   128   0
Minh Byers   68   68   0
Jose R. Cadiz   68   68   0
Natalie A. Calello   277   277   0
Maria Victoria Calica   68   68   0
John Cameron   162   162   0
Susan M. Cannata   96   96   0
Michelle A. Capetillo   68   68   0
Robert C. Capperella   1,127   1,127   0
Korin R. Cardinal   68   68   0
Linda M. Cardone   102   102   0
William M. Carroll   144   144   0
Maria Carter   162   162   0
Jeff Chad   9,425   9,425   0
Louise Chambers   1,939   1,939   0
Jonathan L. Cheney   1,830   1,830   0
Andrew Cheung   56   56   0
Chin Il Choe   83   83   0
Susan Choe   1,663   1,663   0
Barbara Christie-Solomon   831   831   0
Charles J. Clark   222   222   0
Nikki L. Cleaves   162   162   0
Pamela M. Cohen   1,023   1,023   0
Staci C. Coleman   68   68   0

6

Luiza Console   139   139   0
Lawrence Cooney   159   159   0
Sharogerlene Cooper   68   68   0
Thomas A. Cooper   888   888   0
Mary Frances Copeland   271   271   0
Lynda G. Costello   755   755   0
Martina Cousin   554   554   0
Michele A. Craine   635   635   0
Anthony S. Crisci, Jr.   315   315   0
John D. Cronin   169   169   0
David B. Cullinan   184   184   0
Josie Darby   166   166   0
Frank Daspit   4,032   4,032   0
Normarie Davis   15   15   0
James C. Daw   1,719   1,719   0
Sherry A. Deen-Narain   166   166   0
Amy DeLorenzo   90   90   0
Doreen Devine   1,416   1,416   0
Karim Dhanani   928   928   0
Sherry Dineen   477   477   0
Lucas DiPalermo   340   340   0
Lynn W. Dippold   11,088   11,088   0
Thomas J. Dolan   18,672   18,672   0
Thomas P. Dolan   7,208   7,208   0
Ronald J. Dolecki   21,053   21,053   0
Dee Dominick Bradley   1,830   1,830   0
Linda M. Downing   87   87   0
Gertrude E. Downs   510   510   0
Patricia Dowse   166   166   0
Nathan J. Drapkin   484   484   0
Carol Droppa   431   431   0
Babu Dukkipati   332   332   0
Swarna Dukkipati   277   277   0
Douglass S. Dunbar   3,210   3,210   0
Melissa M. Dutcher   318   318   0
Tracy E. Eaton   332   332   0
Steven H. Ellner   4,357   4,357   0
David Engelhaupt   162   162   0
Marybeth Eppig   296   296   0
Christian Eyert   97   97   0
Robert J. Fallon   167   167   0
Robert B. Fane   998   998   0
Karen M. Fanis   68   68   0
Leonard Farrell   340   340   0
Anthony V. Ferraro   2,325   2,325   0
Karen E. Fischer   244   244   0
Franklin L. Fisher   2,786   2,786   0
Morris Fishman   10,395   10,395   0
Teresa Fitzsimmons   28   28   0
Mary P. Flynn   68   68   0

7

Edward W. Fox   7,606   7,606   0
Mark David Frankel   444   444   0
Frank Fratoni   444   444   0
Dee Ann Frawley   880   880   0
David Freeman   2,163   2,163   0
Thomas Freiler   162   162   0
Eddie J. French   68   68   0
Kevin W. Fuller   204   204   0
Kathleen Gail   1,941   1,941   0
Matthew T. Gallardo   68   68   0
Gerald Gallimore   28   28   0
JoAnn Gallimore   106   106   0
Kimberly Gambles   100   100   0
Felix I. Garcia   238   238   0
Samuel Garcia   68   68   0
Sondra Gardiner   714   714   0
Sherilynn Gardner-Pitre   139   139   0
Deanna Gee   1,220   1,220   0
Jeanette R. Gibson   1,830   1,830   0
John J. Gish   168,858   168,858   0
Lane L. Glasgow   1,443   1,443   0
Lawrence Golden   24,143   24,143   0
Raja Gopalan   194   194   0
G. Hart Gordon   1,663   1,663   0
Douglas Gore   28   28   0
Michelle M. Graham   408   408   0
Barbara Gross   435   435   0
Linda Grosso   13,860   13,860   0
Robert Grotyohann   172   172   0
John Grywalski, Jr.   493   493   0
Michael J. Gulotta   207,396   207,396   0
Michael J. Gulotta Jr.   4,763   4,763   0
Eric Haensgen   68   68   0
Daniel A. Hajjar   2,759   2,759   0
Linda E. Hakala   486   486   0
Andrea M. Hall   1,285   1,285   0
Sandra Hallman   1,296   1,296   0
Nancy Halloran   162   162   0
Rodney G. Hannah   514   514   0
Donald P. Harrington   13,696   13,696   0
Roger C. Harris   3,579   3,579   0
Sherman Harris   159   159   0
James B. Harvey   68   68   0
Diann Z. Hatcher   100   100   0
Diane L. Hauschild   375   375   0
Don Hawes   167   167   0
Jane Hawes   12   12   0
Terry W. Hayes   64   64   0
John A. Hebenstreit   2,215   2,215   0
Frederick N. Heidorn   16,632   16,632   0

8

Lenard Henley   68   68   0
David A. Hennessy/Elizabeth R. Hennessy   575   575   0
Ellen Hennessy   10,327   10,327   0
Ellen Hennessy and Frank Daspit   39,943   39,943   0
Diane K. Herwehe   2   2   0
James L. Hess   117,478   117,478   0
Mindy S. Hintelmann   341   341   0
Dennis T. Hirata   2,218   2,218   0
Kevin Ho   1,109   1,109   0
Stephen Hoeffner   10,241   10,241   0
Mark A. Hollis   1,830   1,830   0
Kathleen Holness   5,947   5,947   0
Donna Holt   97   97   0
Wendy W. Hom   4,628   4,628   0
Tsochih Hong   1,185   1,185   0
Thomas C. Hoskins   1,830   1,830   0
Bi-Hwa Huang   83   83   0
Matthew Hucher   315   315   0
Cyrus W. Huneycutt   651   651   0
Chi Heng Hung   3,743   3,743   0
Mandy Hussey   162   162   0
Colin Hwang   264   264   0
Jeannie Hwang   943   943   0
Dennis Hyland   3,326   3,326   0
Pina Infusini   1,608   1,608   0
Gregory Ingle   848   848   0
Barbara Iocca   277   277   0
Sheree Jaeck   22   22   0
Richard Jaffke   3,326   3,326   0
Alexander J. Jaloway   971   971   0
Allen James   4,436   4,436   0
John Jarka   1,155   1,155   0
John T. Jarusiewicz   2,218   2,218   0
Thomas H. Jarusiewicz   318   318   0
Tyler A. Jayroe   4,211   4,211   0
George H. Jelinski   340   340   0
Elaine E. Jennings   16,632   16,632   0
Sujatha Jeyaraman   162   162   0
Steven G. Johnson   618   618   0
Eleanor Jones   8   8   0
Kenneth S. Jones   1,330   1,330   0
Patricia Jones   68   68   0
Shirley Jones   998   998   0
John Joynes   510   510   0
Kathleen A. Jurs   262   262   0
Janice M. Karlson   179   179   0
Suzanne R. Katambwe   554   554   0
Andrea Katz   3,711   3,711   0
Raymond Keane   998   998   0
Adele Kellman   144   144   0

9

Cynthia F. Kelly   318   318   0
Kathleen Kelly   95   95   0
Allyson Kemka   277   277   0
Joseph M. Kemka   21,832   21,832   0
Julia Kent   148   148   0
Abdul S. Kerim   68   68   0
Karen W. Khan Curley   1,023   1,023   0
Elizabeth Khazzam   146   146   0
Richard Kiehn   4   4   0
Kristine A. Klepper   5,544   5,544   0
Bradford Klinck   12,214   12,214   0
Edward Klos   16,634   16,634   0
Erin A. Knoell   56   56   0
Paul L. Koch   2,530   2,530   0
Michael Konarski   169   169   0
Sharon L. Kophanel   2,266   2,266   0
Joanna Kostrzewa   831   831   0
Patricia A. Kowall   340   340   0
Cheryl J. Kramer Rothman   1,577   1,577   0
Ramraj Krishnan   1,386   1,386   0
Linda Kruse   1,663   1,663   0
Hui-Lin Kuo   1,275   1,275   0
Janice C. Kupka   68   68   0
Scott P. Kutcher   139   139   0
Mandy R. Laesch   169   169   0
Louis A. Laffin   56   56   0
Beverly G. Landstrom   42,211   42,211   0
Vanessa Lannert   443   443   0
Troy M. LaRue   117   117   0
Ky T. Le   867   867   0
Martha G. Leahy   68   68   0
James T. Lecher   477   477   0
Paul Lee   683   683   0
Dawn R. Lemke   68   68   0
Helen Leung   139   139   0
Debbie S. Liebeskind   1,012   1,012   0
Wei-Liang Lin   278   278   0
Mary Liscoumb   443   443   0
Henry Lo   166   166   0
Rita L. Lo   1,004   1,004   0
Malaika Lock   68   68   0
Amy L. Loether   11,088   11,088   0
Lynn Lombardo   554   554   0
Lisa Lombardo-Claus   1,386   1,386   0
Kimberly C. Lorenz   169   169   0
Patricia M. Losey   159   159   0
Amy J. Lucks   477   477   0
Thomas E. Luther   486   486   0
James L. Lutrell   238   238   0
Scott J. Macey   1,647   1,647   0

10

Katie J. Maldonado   102   102   0
Sandra D. Malebranche   375   375   0
Robert Malone   1,021   1,021   0
Anthony N. Manganello   68   68   0
Gary Mann   2,653   2,653   0
Melissa R. Manza   318   318   0
Scott Margolin   1,774   1,774   0
Paul F. Marmora   278   278   0
Susan D. Marsh   772   772   0
Marjorie R. Martin   5,544   5,544   0
Michele Mastropolo   4   4   0
Arliss Matich   68   68   0
Shea D. Maultsby   11,088   11,088   0
Michael J. Maxwell   19,678   19,678   0
Kenneth Mayda   971   971   0
Michael Mayhew   162   162   0
Geraldine Mazalewski   159   159   0
Mary E. Mazurek   442   442   0
John McCarthy   1,109   1,109   0
Dorothy McFarland   442   442   0
Eileen McGee   117   117   0
Eileen McGrath   874   874   0
William David McKinnie, III   50,063   50,063   0
Daniel R. McMonagle   29   29   0
Martin Meadow   831   831   0
Thomas W. Meagher   8,419   8,419   0
Christopher Mealin   17   17   0
Henry J. Mealin   5,524   5,524   0
John Mealin   4,353   4,353   0
Jillian Medoff   453   453   0
Elizabeth A. Mendola   350   350   0
Carmen Metcalfe   139   139   0
Nancy J. Mienhardt   1,160   1,160   0
Alice Miller   340   340   0
Daniel Miller   8,871   8,871   0
David C. Miller   2,117   2,117   0
John J. Miller   56,674   56,674   0
Monika Minor   162   162   0
Lawrence A. Moellers   110   110   0
Theresa A. Mohr   1,164   1,164   0
Kenneth C. Morgan   29,979   29,979   0
Nancy K. Mueller   68   68   0
Arthur Murphy   1,079   1,079   0
John Murphy   2,771   2,771   0
Sandra B. Murray   11   11   0
David Myles   166   166   0
Sujatha Nampalli   68   68   0
Christopher A. Narcisco   64   64   0
Wendy A. Neal   945   945   0
Glen C. Nebel   1,986   1,986   0

11

Paul M. Nelson   68   68   0
Jonathan Nemeth   26,367   26,367   0
John Nestico   4,638   4,638   0
Khanh Nguyen   179   179   0
Andrzej T. Niewiadomski   2,218   2,218   0
Mien H. Niu   1,333   1,333   0
Thomas E. Norton   24,388   24,388   0
Maritza L. Nowakowski   2,486   2,486   0
Denise B. O'Bara   95   95   0
Jessica M. Occhino   186   186   0
George F. O'Donnell   23,293   23,293   0
Florence O. Odufu   68   68   0
Femi O. Odulana   1,663   1,663   0
Christine M. Olhava-Ablin   34   34   0
Elizabeth A. Olson   2,218   2,218   0
Linda Orr   720   720   0
Alan Oskowsky   1,968   1,968   0
John O'Sullivan   5,493   5,493   0
Dorothy M. Ott   203   203   0
Stanislaw Pade   1,369   1,369   0
Joseph J. Pagano   1,830   1,830   0
Brenda Page    97   97   0
Janna M. Paolino   68   68   0
Thomas J. Parciak   15,727   15,727   0
John C. Parr   3,623   3,623   0
Timothy Parris   28   28   0
Raymount Paschal   12   12   0
Ankita M. Patel   68   68   0
Margi Patel   68   68   0
Joseph Paterno   333   333   0
Dean Pedretti   19   19   0
Maria L. Perez   8   8   0
Auburn Perkins   4   4   0
Raymond Perry   1,220   1,220   0
Shannon Perry-Tucker   120   120   0
Gina Petrone-Mumolie   1,663   1,663   0
Stephanie Pfeiffer   31   31   0
Thi M. Pham   95   95   0
Linda S. Phillips   442   442   0
Marklyn W. Pierre   68   68   0
Vinita Pilani   194   194   0
Luc Pomerleau   244   244   0
Khuzema Poonawala   68   68   0
Dylan Porter   4,436   4,436   0
David P. Previte   251   251   0
Doug L. Pryor   1,539   1,539   0
Amin Purshottam   554   554   0
Ann Rachel Quesada   43,270   43,270   0
Antonio P. Quesada   2,079   2,079   0
Kathleen A. Quinn   34   34   0

12

Vivian V. Quintanilla   31   31   0
Hugh R. Raines   8   8   0
Jennifer Rambusch   357   357   0
Neela K. Ranade   8,944   8,944   0
Joi Randall   277   277   0
Christine Randle   609   609   0
Otis C. Ray   6,737   6,737   0
Mary Elizabeth Redding   6,748   6,748   0
Robert Reddington   56,288   56,288   0
Rebecca W. Redman   2,495   2,495   0
Susan M. Rees   11   11   0
W. Mitchell Rees   9,703   9,703   0
Anne M. Reminger   159   159   0
Leslie H. Richmond   16,467   16,467   0
Nicole A. Rickmond   266   266   0
Judith Ringlein-Dunn   204   204   0
Calvin R. Roberson   68   68   0
Elizabeth Robinson   190   190   0
Jeffrey Robinson   5,544   5,544   0
John T. Rock   296   296   0
Mary C. Romash   11   11   0
Beverly S. Rose   13,860   13,860   0
Donna L. Rose   225   225   0
Mark Rosenberg   2,577   2,577   0
Rachel Rosengard   16   16   0
Lester J. Rosensaft   190,976   190,976   0
Randall Roth   1,142   1,142   0
Allen J. Rothman   46,251   46,251   0
Wanda Russell   971   971   0
Gordon Rutledge   4,436   4,436   0
Jack Sabley   190   190   0
Sylvia Sae   342   342   0
Rafael Sanchez   974   974   0
Benjamin J. Sandborg   554   554   0
Antonietta Sartor   79   79   0
Ingalill Saxena   1,666   1,666   0
John Scala   1,494   1,494   0
Cheryllee Schachel   477   477   0
Rita L. Schmieder   68   68   0
Estate of Clarin S. Schwartz   51,123   51,123   0
Barry K. Schwebs   1,278   1,278   0
Karen A. Sefcik   6,376   6,376   0
Frank B. Senese   128   128   0
Deborah J. Sessoms   780   780   0
Kelly Shah   8,871   8,871   0
Amy Sham   1,150   1,150   0
Sherry Shaw-Kobee   554   554   0
Yelena Shchekina   169   169   0
Brian R. Shepherd   12   12   0
Donna Sherratt-Bado   238   238   0

13

Mary-Catherine Shiflett   2,218   2,218   0
Stephen H. Shub   833   833   0
Jefferson T. Simmons   102   102   0
Michelle M. Sims   4   4   0
Scott B. Singhass   169   169   0
Richard C. Skibinski   68   68   0
Craig S. Smith   169   169   0
Gerald Smith   1,663   1,663   0
Kenyata Smith   68   68   0
James M. Smitreski   5,277   5,277   0
Leslie K. Soo Hoo   8,871   8,871   0
Maribel Soto   159   159   0
Matthew Spicer   162   162   0
Vicki Squire-Hall   190   190   0
Vincent Stesner   1,241   1,241   0
William F. Stopa   976   976   0
Ellen Stuckey   53   53   0
Stephanie L. Sturm   68   68   0
Alene Styles-Glover   1,031   1,031   0
Lisa Stylianou   28   28   0
Warren P. Suggs   1,663   1,663   0
Eric Summers   1,830   1,830   0
Ying Loi Sung   3,326   3,326   0
Jon D. Sutcliffe   7,374   7,374   0
John Swaney   554   554   0
Rezzelline Tan   166   166   0
Nancy M. Tartaro   18,166   18,166   0
Chris D. Taylor   4   4   0
Valencia Taylor   28   28   0
James Teasley   323   323   0
Nancy Thacker   1,109   1,109   0
Juna Thelemaque   8   8   0
Raymond N. Thomas   2,748   2,748   0
Andrew W. Thompson   2,818   2,818   0
Sani Timbadia   318   318   0
Sharon Tomita   1,663   1,663   0
Pamela Y. Toussaint   3,471   3,471   0
Ollie Treadway   4,616   4,616   0
Louis Tremblay   21   21   0
Marie Frances Trometer   340   340   0
Thau-Yung Tsao   56   56   0
Alan Turetz   10,701   10,701   0
Andrzej Tyminski   998   998   0
Christine J. Ubertaccio   3,579   3,579   0
Richard Vair   9,273   9,273   0
April H. Valerio   162   162   0
Lynda Van Hoorn   277   277   0
Douglas Varga   1,830   1,830   0
Vinod Vedvyas   2,771   2,771   0
Ada C. Villahermosa   28   28   0

14

Lucretia Benee Vinson   2   2   0
Aimee L. Viola   29,158   29,158   0
Marie Vladic   68   68   0
F. Randy Vogenberg   11,088   11,088   0
Shawn C. Vollmann   340   340   0
Robert Wagner   1,497   1,497   0
Elaine Walsh   1,109   1,109   0
Augustine Wan   604   604   0
Bor-Sing Wang   2,294   2,294   0
Edward D. Ward   554   554   0
Mary M. Ward   5,991   5,991   0
Kimberly C. Warwick   150   150   0
Eddie R. Watson II   350   350   0
James W. Wells   2,412   2,412   0
Kenneth R. Wells   888   888   0
Vernetta S. Wells   194   194   0
Michael J. Whalen   169   169   0
Amie D. White   169   169   0
Jeanne Whitmore   95   95   0
James R. Wiggins   1,386   1,386   0
Jennifer J. Wikstrom   88   88   0
Henry B. Wilantewicz III   186   186   0
B. Jill Wilkinson   277   277   0
Thomas J. Will   1,654   1,654   0
Jacqueline Williams   68   68   0
Patricia I. Wilner   1,386   1,386   0
Lawrence F. Wilson   8,316   8,316   0
Hoi Shun Wong   95   95   0
Michael G. Worthen   162   162   0
Hugh L. Worthington   204   204   0
Harry Wright   18,382   18,382   0
Philip Wright   17,083   17,083   0
Suzanne C. Wyatt   1,830   1,830   0
Maryann Yim   1,663   1,663   0
David P. York   1,386   1,386   0
Gretchen K. Young   4,452   4,452   0
Thomas M. Zavist   4,030   4,030   0
Kelley Zittinger   162   162   0
   
       
    2,395,072        
   
       

15


PLAN OF DISTRIBUTION

        We will receive no part of the proceeds of any sales made hereunder. We will pay all expenses of registration incurred in connection with this offering and in connection with the offering and sale of the shares, other than commissions, discounts and fees of underwriters, dealers or agents. All selling and other expenses incurred by the selling stockholders will be borne by the selling stockholders.

        The selling stockholders and any broker-dealers participating in the distribution of the shares may be deemed to be "underwriters" within the meaning of the Securities Act of 1933, and any commissions or discounts given to any such broker-dealer may be regarded as underwriting commissions or discounts under that Act.

        The selling stockholders may from time to time sell all or a portion of the shares on the New York Stock Exchange or on any national securities exchange on which our common stock may be listed or traded, in negotiated transactions or otherwise, at prices then prevailing or related to the then current market price or at negotiated prices. The shares will not be sold in an underwritten public offering. The shares may be sold directly or through brokers or dealers. The methods by which the shares may be sold include:

        (1)  a block trade (which may involve crosses) in which the broker or dealer so engaged will attempt to sell the shares as agent but may position and resell a portion of the block as principal to facilitate the transaction;

        (2)  purchases by a broker or dealer as principal and resale by such broker or dealer for its account pursuant to this prospectus;

        (3)  ordinary brokerage transactions and transactions in which the broker solicits purchasers; and

        (4)  privately negotiated transactions.

        In effecting sales, brokers and dealers engaged by the selling stockholders may arrange for other brokers or dealers to participate. Brokers or dealers may receive commissions or discounts from the selling stockholders (or, if any such broker-dealer acts as agent for the purchaser of such shares, from such purchaser) in amounts to be negotiated which are not expected to exceed those customary in the types of transactions involved. Broker-dealers may agree with the selling stockholders to sell a specified number of such shares at a stipulated price per share, and, to the extent such broker-dealer is unable to do so acting as agent for a selling stockholder, to purchase as principal any unsold shares at the price required to fulfill the broker-dealer commitment to such selling stockholder. Broker-dealers who acquire shares as principal may thereafter resell such shares from time to time in transactions (which may involve crosses and block transactions and sales to and through other broker-dealers, including transactions of the nature described above) in the over-the-counter market or otherwise at prices and on terms then prevailing at the time of sale, at prices then related to the then-current market price or in negotiated transactions and, in connection with such resales, may receive from the purchasers of such shares commissions as described above.

        In connection with the distribution of the shares, the selling stockholders may enter into hedging transactions with broker-dealers. In connection with such transactions, broker-dealers may engage in short sales of the shares in the course of hedging the positions they assume with the selling stockholders. The selling stockholders may also sell the shares short and redeliver the shares to close out the short positions. The selling stockholders may also enter into option or other transactions with broker-dealers, which require the delivery to the broker-dealer of the shares. The selling stockholders may also loan or pledge the shares to a broker-dealer and the broker-dealer may sell the shares so loaned or upon a default the broker-dealer may effect sales of the pledged shares. In addition to the foregoing, the selling stockholders may enter into, from time to time, other types of hedging transactions.

16


        The selling stockholders and any broker-dealers participating in the distributions of the shares may be deemed to be "underwriters" within the meaning of Section 2(11) of the Securities Act of 1933 and any profit on the sale of shares by the selling stockholders and any commissions or discounts given to any such broker-dealer may be deemed to be underwriting commissions or discounts under that Act.

        In addition, any shares covered by this prospectus that qualify for sale pursuant to Rule 144 may be sold under Rule 144 under the Securities Act rather than pursuant to this prospectus.


LEGAL MATTERS

        The validity of the securities will be passed upon for us by Richard E. Barry, our Senior Counsel and Assistant Secretary. As of October 8, 2002, Mr. Barry owned 5,117 shares of Aon Corporation common stock, held restricted stock awards of 24,600 shares and 1,980 vested and 24,020 unvested stock options. In addition, 2,682 shares of Aon Corporation common stock held by its employee stock ownership plan and savings plan were attributable to Mr. Barry.


EXPERTS

        The consolidated financial statements and the related financial statement schedules (as restated) of Aon Corporation included in Aon Corporation's Annual Report (Form 10-K/A) for the year ended December 31, 2001 have been audited by Ernst & Young LLP, independent auditors, as set forth in their report thereon included therein and incorporated herein by reference. Such consolidated financial statements and schedules are incorporated herein by reference in reliance upon such report given on the authority of such firm as experts in accounting and auditing.

        With respect to the unaudited condensed consolidated interim financial information for the three-month periods ended March 31, 2002 and March 31, 2001, and the three and six-month periods ended June 30, 2002 and June 30, 2001, incorporated by reference in this prospectus, Ernst & Young LLP have reported that they have applied limited procedures in accordance with professional standards for a review of such information. However, their separate reports, included in Aon Corporation's Quarterly Reports on Forms 10-Q/A and Form 10-Q for the quarters ended March 31, 2002 and June 30, 2002, respectively, and incorporated herein by reference, state that they did not audit and they do not express an opinion on that interim financial information. Accordingly, the degree of reliance on their reports on such information should be restricted considering the limited nature of the review procedures applied. The independent auditors are not subject to the liability provisions of Section 11 of the Securities Act of 1933 (the "Act") for their reports on the unaudited interim financial information because those reports are not a "report" or a "part" of the Registration Statement prepared or certified by the auditors within the meaning of Sections 7 and 11 of the Act.

17



PART II

INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14. Other Expenses of Issuance and Distribution.*

Securities and Exchange Commission registration fee   $ 1,167
Accounting fees     5,000
Printing, distribution, and engraving fees     5,000
Legal fees and expenses     15,000
Miscellaneous     333
   
  Total   $ 26,500
   
*
All amounts are estimated except for the Securities and Exchange Commission registration fee.


Item 15. Indemnification of Directors and Officers.

        The registrant was organized under and is subject to the Delaware General Corporation Law. Delaware law provides that officers and directors may receive indemnification from their corporations for certain actual or threatened lawsuits. The Delaware law sets out the standard of conduct which the officers and directors must meet in order to be indemnified, the parties who are to determine whether the standard has been met, and the types of expenditures which will be indemnified. Delaware law further provides that a corporation may purchase indemnification insurance, such insurance providing indemnification for the officers and directors whether or not the corporation would have the power to indemnify them against such liability under the provisions of Delaware law.

        The registrant has adopted an article within its second restated certificate of incorporation, as amended, which provides that it will indemnify its officers and directors to the full extent permitted by Delaware law.

        Furthermore, the registrant is covered by insurance which will reimburse it within the policy limits for amounts it is obligated to pay in lawsuits involving officers and directors serving in such capacities in which the damages, judgments, settlements, costs, charges or expenses incurred in connection with the defense of the action, suit or proceeding are reimbursable pursuant to the law and the second restated certificate of incorporation, as amended.


Item 16. Exhibits.

        Exhibits marked with an asterisk (*) are incorporated by reference to documents previously filed by the registrant with the Securities and Exchange Commission, as indicated. All other documents listed are or will be filed with this registration statement.

Number
   Description
*2(a)   Agreement and Plan of Merger dated as of August 22, 2000 between the registrant, Aon Keith Acquisition Corp. and ASA Acquisition Corp. incorporated by reference to Exhibit 2(a) to the registrant's Registration Statement on Form S-3 (SEC File No. 333-49300).

*2(b)
 
Registration Rights Agreement dated as of October 2, 2000 between the registrant and Ellen A. Hennessy, as the stockholders' representative incorporated by reference to Exhibit 2(b) to the registrant's Registration Statement on Form S-3 (SEC File No. 333-49300).

 
 
 

II-1


*3(a)
 
Second Restated Certificate of Incorporation of the registrant incorporated by reference to Exhibit 3(a) to the registrant's Annual Report on Form 10-K for the year ended December 31, 1991.

*3(b)
 
Certificate of Amendment of the registrant's Second Restated Certificate of Incorporation incorporated by reference to Exhibit 3 to the registrant's Quarterly Report on Form 10-Q for the quarter ended March 31, 1994.

*3(c)
 
Certificate of Amendment of the registrant's Second Restated Certificate of Incorporation incorporated by reference to Exhibit 3 to the registrant's Current Report on Form 8-K, dated May 9, 2000.

*3(d)
 
Amended By-laws of the registrant incorporated by reference to Exhibit 3.2 to the registrant's Current Report on Form 8-K filed October 4, 2002.

*3(e)
 
Certificate of Designation for the registrant's Series C Cumulative Preferred Stock incorporated by reference to Exhibit 4.1 to the registrant's Current Report on Form 8-K, dated February 9, 1994.

5
 
Opinion of Richard E. Barry, Senior Counsel and Assistant Secretary of the registrant.

23(a)
 
Consent of Richard E. Barry (included in Exhibit 5).

23(b)
 
Consent of Ernst & Young LLP.

23(c)
 
Acknowledgement of Ernst & Young LLP.

24
 
Powers of Attorney.


Item 17. Undertakings.

        The registrant hereby undertakes:

II-2

II-3


SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing this registration statement on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the City of Chicago, State of Illinois, as of October 9, 2002.

    AON CORPORATION

 
 
By:
 
/s/  PATRICK G. RYAN      
Patrick G. Ryan
Chairman and Chief Executive Officer

        Pursuant to the requirements of the Securities Act of 1933, this registration statement has been signed below by the following persons in the capacities indicated as of October 9, 2002.

Signature
   Capacity

 
 
 

/s/  PATRICK G. RYAN      
Patrick G. Ryan
 
Chairman, Chief Executive Officer and Director
(Principal Executive Officer)

/s/  HARVEY N. MEDVIN      
Harvey N. Medvin
 
Executive Vice President and Chief Financial Officer
(Principal Financial and Accounting Officer)


*
Edgar D. Jannotta

 

Director

*
Lester B. Knight
 
Director

*
Perry J. Lewis
 
Director

*
R. Eden Martin
 
Director

*
Andrew J. McKenna
 
Director

*
Robert S. Morrison
 
Director

*
Richard C. Notebaert
 
Director

*
Michael D. O'Halleran
 
President, Chief Operating Officer and Director

 
 
 

II-4


*
John W. Rogers, Jr.
 
Director

*
Patrick G. Ryan, Jr.
 
Director

*
George A. Schaefer
 
Director

/s/  RAYMOND I. SKILLING      
Raymond I. Skilling
 
Executive Vice President, Chief Counsel and Director

*
Carolyn Y. Woo
 
Director

*By:
 
/s/  RAYMOND I. SKILLING      
Raymond I. Skilling
 Attorney-in-Fact
 
 
 
 

Date: October 9, 2002

II-5


EXHIBIT INDEX

TO REGISTRATION STATEMENT
ON FORM S-3

AON CORPORATION

Exhibit
Number
   Description of Exhibit
*2(a)   Agreement and Plan of Merger dated as of August 22, 2000 between the registrant, Aon Keith Acquisition Corp. and ASA Acquisition Corp. incorporated by reference to Exhibit 2(a) to the registrant's Registration Statement on Form S-3 (SEC File No. 333-49300).

*2(b)
 
Registration Rights Agreement dated as of October 2, 2000 between the registrant and Ellen A. Hennessy, as the stockholders' representative. incorporated by reference to Exhibit 2(b) to the registrant's Registration Statement on Form S-3 (SEC File No. 333-49300).

*3(a)
 
Second Restated Certificate of Incorporation of the registrant incorporated by reference to Exhibit 3(a) to the registrant's Annual Report on Form 10-K for the year ended December 31, 1991.

*3(b)
 
Certificate of Amendment of the registrant's Second Restated Certificate of Incorporation incorporated by reference to Exhibit 3 to the registrant's Quarterly Report on Form 10-Q for the quarter ended March 31, 1994.

*3(c)
 
Certificate of Amendment of the registrant's Second Restated Certificate of Incorporation incorporated by reference to Exhibit 3 to the registrant's Current Report on Form 8-K, dated May 9, 2000.

*3(d)
 
Amended By-laws of the registrant incorporated by reference to Exhibit 3.2 to the registrant's Current Report on Form 10-K for the year ended December 31, 1982.

*3(e)
 
Certificate of Designation for the registrant's Series C Cumulative Preferred Stock incorporated by reference to Exhibit 4.1 to the registrant's Current Report on Form 8-K dated February 9, 1994.

5
 
Opinion of Richard E. Barry, Senior Counsel and Assistant Secretary of the registrant.

23(a)
 
Consent of Richard E. Barry (included in Exhibit 5).

23(b)
 
Consent of Ernst & Young LLP.

23(c)
 
Acknowledgement of Ernst & Young LLP.

24
 
Powers of Attorney.

Exhibits marked with an asterisk (*) are incorporated by reference to documents previously filed by the registrant with the Securities and Exchange Commission, as indicated.



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TABLE OF CONTENTS
WHERE YOU CAN FIND MORE INFORMATION
SPECIAL NOTE ON FORWARD-LOOKING STATEMENTS
THE COMPANY
THE OFFERING
USE OF PROCEEDS
SELLING STOCKHOLDERS
PLAN OF DISTRIBUTION
LEGAL MATTERS
EXPERTS
PART II INFORMATION NOT REQUIRED IN PROSPECTUS
SIGNATURES
EXHIBIT INDEX TO REGISTRATION STATEMENT ON FORM S-3 AON CORPORATION