Aon plc — Director's Dealing 2011

May 24, 2011

SEC Form 4 — Statement of Changes in Beneficial Ownership

Issuer: AON CORP (AOC)
CIK: 0000315293
Period of Report: 2011-05-20

Reporting Person: KNIGHT LESTER B (Director)

Derivative Transactions

Date	Security	Exercise Price	Code	Shares	A/D	Expiration	Underlying	Ownership
2011-05-20	Deferred Stock Units	$	A	2010.34	Acquired		Common Stock (2010.34)	Direct
2011-05-20	Deferred Stock Units	$	A	3829.217	Acquired		Common Stock (3829.217)	Direct
2011-05-20	Phantom Stock	$	A	526.518	Acquired		Common Stock (526.518)	Direct

Footnotes

F1: The deferred stock units convert to shares of common stock on a 1-for-1 basis.

F2: The deferred stock units represent an outside director stock award granted annually to each non-employee director of Aon Corporation.

F3: The deferred stock units vest over a one-year period, and will convert to and be paid in shares of Aon common stock upon the earlier of: (a) the third anniversary of the date of grant; or (b) the director's termination of service from the Board, unless a timely deferral election is made.

F4: Includes shares acquired pursuant to dividend reinvestment.

F5: The deferred stock units represent a stock award granted to the reporting person for his service as non-Executive Chairman of Aon Corporation.

F6: The phantom stock units convert to shares of common stock on a 1-for-1 basis.

F7: The phantom stock units represent an outside director fee that was deferred into a directors' deferred compensation arrangement. A portion of the fee was received for acting as chairperson of a Board Committee.

F8: The phantom stock units will be paid in cash or shares of Aon common stock on a distribution date elected by the reporting person.

F9: Includes shares acquired pursuant to dividend reinvestment.