Sec Form 4 Filing - OHALLERAN MICHAEL D @ AON CORP - 2007-08-15

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 OHALLERAN MICHAEL D 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) Senior Exec VP (Last) (First) (Middle) AON CORPORATION - CORPORATE LAW DEPT, 200 EAST RANDOLPH STREET, 8TH FLOOR 3. Date of Earliest Transaction (MM/DD/YY) 08/15/2007 (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

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 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 Employee Stock Option (Right to Buy) $ 36.875 08/15/2007 D 120,000 ( 1 )( 2 ) 04/22/2012 Common Stock 120,000 ( 1 ) ( 2 ) 0 D Employee Stock Option (Right to Buy) $ 39.25 08/15/2007 A 120 ,000 ( 1 )( 2 ) 04/22/2012 Common Stock 120,000 ( 1 ) ( 2 ) 120,000 D

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other OHALLERAN MICHAEL D AON CORPORATION - CORPORATE LAW DEPT 200 EAST RANDOLPH STREET, 8TH FLOOR CHICAGO, IL60601 Senior Exec VP Signatures /s/ Jennifer L. Kraft - by Jennifer L. Kraft pursuant to a power of attorney from Michael D. O'Halleran 08/17/2007 Signature of Reporting Person Date

Explanation of Responses:

( 1 )In a Form 5 filed in February 2003, the reporting person reported that, on April 22, 2002, he was granted an employee stock option covering 120,000 shares of common stock, having an exercise price of $36.8750 per share and vesting in three annual installments beginning on April 22, 2004. Following a review of the issuer's stock option award practices, it was determined that the exercise price for this option should be adjusted to $39.250 per share to reflect the fair market value of the issuer's common stock on the accounting measurement date. As a result, the reporting person and the issuer agreed to amend the option to provide that the option will have an exercise price of $39.250 per share. ( 2 )All other terms and conditions of the option award remain the same, including the vesting schedule described above. The amendment is reported in this Form 4 as a cancellation of the original option and the grant of a replacement option. For additional information, please see the issuer's Current Report on Form 8-K, which was filed with the Commission on August 15, 2007

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* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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