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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
 Q+ZoLdft8MBcjOar1YOXLd4K7V2LYsJeaER2eRGoZy+k5+fGhYvUUsBitgPmEF+N
 xJarPg1jYJyor2LRxYiYbQ==

<SEC-DOCUMENT>0001179110-07-010933.txt : 20070522
<SEC-HEADER>0001179110-07-010933.hdr.sgml : 20070522
<ACCEPTANCE-DATETIME>20070522170323
ACCESSION NUMBER:		0001179110-07-010933
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20070518
FILED AS OF DATE:		20070522
DATE AS OF CHANGE:		20070522

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			KALFF JAN
		CENTRAL INDEX KEY:			0001247425

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07933
		FILM NUMBER:		07871720

	MAIL ADDRESS:	
		STREET 1:		AON CORP
		STREET 2:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601

	FORMER NAME:	
		FORMER CONFORMED NAME:	KALFF PF
		DATE OF NAME CHANGE:	20030625

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			AON CORP
		CENTRAL INDEX KEY:			0000315293
		STANDARD INDUSTRIAL CLASSIFICATION:	ACCIDENT & HEALTH INSURANCE [6321]
		IRS NUMBER:				363051915
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601
		BUSINESS PHONE:		3123811000

	MAIL ADDRESS:	
		STREET 1:		200 EAST RANDOLPH STREET
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	COMBINED INTERNATIONAL CORP
		DATE OF NAME CHANGE:	19870504
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-05-18</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000315293</issuerCik>
        <issuerName>AON CORP</issuerName>
        <issuerTradingSymbol>AOC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001247425</rptOwnerCik>
            <rptOwnerName>KALFF JAN</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>AON CORPORATION - CORPORATE LAW DEPT</rptOwnerStreet1>
            <rptOwnerStreet2>200 EAST RANDOLPH STREET, 8TH FLOOR</rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60601</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable></nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Deferred Stock Units</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F1"/>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2007-05-18</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1944.64</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2007-05-18</value>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F3"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1944.64</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4325.23</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">The deferred stock units convert to shares of common stock on a 1-for-1 basis.</footnote>
        <footnote id="F2">The deferred stock units represent an outside director stock award granted annually to each non-employee director of Aon Corporation.</footnote>
        <footnote id="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.</footnote>
        <footnote id="F4">Includes shares acquired pursuant to dividend reinvestment.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jennifer L. Kraft - by Jennifer L. Kraft pursuant to a power of attorney from Jan Kalff</signatureName>
        <signatureDate>2007-05-22</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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