FORM 4 Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940

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(Print or Type Responses)

1. Name and Address of Reporting Person * MCKENNA ANDREW J   2. Issuer Name and Ticker or Trading Symbol AON CORP [AOC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) __X__ Director _____ 10% Owner _____ Officer (give title below) _____ Other (specify below) (Last) (First) (Middle) AON CORPORATION - CORPORATE LAW DEPT, 200 EAST RANDOLPH STREET, 8TH FLOOR 3. Date of Earliest Transaction (Month/Day/Year) 05/20/2005 (Street) CHICAGO, IL 60601 4. If Amendment, Date Original Filed(Month/Day/Year) 6. Individual or Joint/Group Filing(Check Applicable Line) _X_ Form filed by One Reporting Person ___ Form filed by More than One Reporting Person (City) (State) (Zip) Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned

1.Title of Security (Instr. 3) 2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code (Instr. 8) 4. Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5) 5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4) 6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4) 7. Nature of Indirect Beneficial Ownership (Instr. 4) Code V Amount (A) or (D) Price

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)

1. Title of Derivative Security (Instr. 3)

2. Conversion or Exercise Price of Derivative Security

3. Transaction Date (Month/Day/Year)

3A. Deemed Execution Date, if any (Month/Day/Year)

4. Transaction Code (Instr. 8)

5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4, and 5)

6. Date Exercisable and Expiration Date (Month/Day/Year)

7. Title and Amount of Underlying Securities (Instr. 3 and 4)

8. Price of Derivative Security (Instr. 5)

9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)

10. Ownership Form of Derivative Security: Direct (D) or Indirect (I) (Instr. 4)

11. Nature of Indirect Beneficial Ownership (Instr. 4)

Code

V

(A)

(D)

Date Exercisable

Expiration Date

Title

Amount or Number of Shares

Phantom Stock

(1)

05/20/2005

A

302.297 (2)

05/20/2005

(3)

Common Stock

302.297

(2)

54,162.382

D

Phantom Stock

(1)

05/20/2005

A

2,136 (4)

05/20/2005

(5)

Common Stock

2,136

(4)

18,790.051

D

Phantom Stock

(1)

05/20/2005

A

1,309.956 (6)

05/20/2005

(7)

Common Stock

1,309.956

(6)

12,974.547

D

Reporting Owners

Reporting Owner Name / Address	Relationships
	Director	10% Owner	Officer	Other
MCKENNA ANDREW J AON CORPORATION - CORPORATE LAW DEPT 200 EAST RANDOLPH STREET, 8TH FLOOR CHICAGO, IL 60601	X

Signatures

/s/ Jennifer L. Kraft - by Jennifer L. Kraft pursuant to a power of attorney from Andrew J. McKenna		05/24/2005
**Signature of Reporting Person		Date

Explanation of Responses:

*	If the form is filed by more than one reporting person, see Instruction 4(b)(v).
**	Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1)	The phantom stock units convert to shares of common stock on a 1 for 1 basis.
(2)	The phantom stock units represent an outside director fee that was deferred into a directors' deferred compensation arrangement.
(3)	The phantom stock units will be paid in cash or Aon Corporation common stock on a distribution date elected by the reporting person.
(4)	The phantom stock units represent an outside director stock award granted annually to each non-employee director of Aon Corporation.
(5)	The phantom stock units will be paid in Aon Corporation common stock on a distribution date elected by the reporting person.
(6)	The phantom stock units represent amounts credited to a directors' retirement account on behalf of each outside director.
(7)	The phantom stock units will be paid in Aon Corporation common stock in ten annual installments upon retirement, death or disability.

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