Sec Form 4 Filing - MAHONEY DENNIS L @ AON CORP - 2007-03-15

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 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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1. Name and Address of Reporting Person MAHONEY DENNIS L 2. Issuer Name and Ticker or Trading Symbol AON CORP [ AOC] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) _____ Director _____ 10% Owner X __ Officer (give title below) _____ Other (specify below) Aon Limited - Chairman/CEO (Last) (First) (Middle) AON CORPORATION - CORPORATE LAW DEPT, 200 EAST RANDOLPH STREET, 8TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 03/15/2007 (Street) CHICAGO, IL60601 4. If Amendment, Date Original Filed (MM/DD/YY) 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 (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 Common Stock 03/16/2007 M( 1 ) 1,394 A 14,883 D Common Stock 03/16/2007 F( 2 ) 572 D $ 37.82 14,311 D Common Stock 03/17/2007 M( 1 ) 1,865 A 16,176 D Common Stock 03/17/2007 F( 2 ) 765 D $ 37.82 15,411 D Common Stock 4,996 I Through Aon Savings Plan and ESOP

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 7. Title and Amount of Underly ing 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 Employee Stock Option (Right to Buy) $ 37.1 03/15/2007 A 30,324 ( 3 ) 03/15/2013 Common Stock 30,324 ( 4 ) 30,324 D Restricted Stock Unit Award (Right to Receive) ( 5 ) 03/16/2007 M 1,394 03/16/2007 03/16/2007 Common Stock 1,394 $ 0 4,662 D Restricted Stock Unit Award (Right to Receive) ( 5 ) 03/17/2007 M 1,865 03/17/2007 03/17/2007 Common Stock 1,865 $ 0 4,877 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other MAHONEY DENNIS L AON CORPORATION - CORPORATE LAW DEPT 200 EAST RANDOLPH STREET, 8TH FLOOR CHICAGO, IL60601 Aon Limited - Chairman/CEO Signatures /s/ Jennifer L. Kraft - Jennifer L. Kraft pursuant to a power of attorney from Dennis L. Mahoney 03/19/2007 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Shares of common stock acquired upon the vesting of a restricted stock unit award. ( 2 )Shares of common stock withheld by the issuer for the payment of withholding taxes in connection with the vesting of a restricted stock unit award. ( 3 )Vesting will occur in accordance with the terms of the Aon Stock Incentive Plan as follows: one-third of the options will vest on each of the first through third anniversaries of the date of grant. ( 4 )Stock option granted pursuant to the Aon Stock Incentive Plan. ( 5 )The restricted stock unit award converts to shares of common stock on a 1-for-1 basis.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* 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).

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