-----BEGIN PRIVACY-ENHANCED MESSAGE-----
Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 DJBLMG6VoYH/SF2QBKrRRrGPpWRUbgb073iaQYvz/tPBZzcBHaeE+voh5e3l7F2F
 YvawESRPV1BzZ9z9w/Ehbg==

<SEC-DOCUMENT>0001179110-08-015067.txt : 20080811
<SEC-HEADER>0001179110-08-015067.hdr.sgml : 20080811
<ACCEPTANCE-DATETIME>20080811204512
ACCESSION NUMBER:		0001179110-08-015067
CONFORMED SUBMISSION TYPE:	3/A
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20080401
FILED AS OF DATE:		20080811
DATE AS OF CHANGE:		20080811

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

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			Hayley Kathryn
		CENTRAL INDEX KEY:			0001431838

	FILING VALUES:
		FORM TYPE:		3/A
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-07933
		FILM NUMBER:		081007983

	BUSINESS ADDRESS:	
		BUSINESS PHONE:		312.381.5115

	MAIL ADDRESS:	
		STREET 1:		C/O AON CORPORATION, LAW DEPT
		STREET 2:		200 EAST RANDOLPH STREET, 8TH FLOOR
		CITY:			CHICAGO
		STATE:			IL
		ZIP:			60601
</SEC-HEADER>
<DOCUMENT>
<TYPE>3/A
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 3/A -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0203</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2008-04-01</periodOfReport>

    <dateOfOriginalSubmission>2008-04-10</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001431838</rptOwnerCik>
            <rptOwnerName>Hayley Kathryn</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>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>ACW - Chief Executive Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1131</value>
                    <footnoteId id="F5"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeHolding>
            <securityTitle>
                <value>Restricted Stock Unit Award (Right to Receive)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2011-06-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>80000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Restricted Stock Unit Award (Right to Receive)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F3"/>
            </exerciseDate>
            <expirationDate>
                <value>2010-03-15</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>4088</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Employee Stock Option (Right to Buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>33.345</value>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2016-06-14</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>100000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Restricted Stock Unit Award (Right to Receive)</value>
                <footnoteId id="F7"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F2"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F6"/>
            </exerciseDate>
            <expirationDate>
                <value>2011-03-13</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>7211</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Awards granted pursuant to the Aon Stock Incentive Plan that will vest as follows: one-third of the awards will vest on each of the third through fifth anniversaries of the date of grant.  The date of grant was June 14, 2006.</footnote>
        <footnote id="F2">The restricted stock unit award converts to shares of common stock on a 1-for-1 basis.</footnote>
        <footnote id="F3">Awards granted pursuant to the Aon Stock Incentive Plan that will vest as follows:  22.22% of the awards will vest on each of the first and second anniversaries of the date of grant, and 55.56% of the awards will vest on the third anniversary of the date of grant.  The date of grant was March 15, 2007, and the amount of the initial grant was 5,257 restricted stock units, 1,169 of which have previously vested.</footnote>
        <footnote id="F4">Options granted pursuant to the Aon Stock Incentive Plan that will vest as follows:  one-third of the options will vest on each of the second through fourth anniversaries of the date of grant.  The date of grant was June 14, 2006.</footnote>
        <footnote id="F5">Includes 312 shares held through the Aon employee stock purchase plan.  These shares were inadvertently omitted from the original filing due to an adminstrative error.</footnote>
        <footnote id="F6">Awards granted pursuant to the Aon Stock Incentive Plan that will vest as follows:  one-third of the awards will vest on each of the first through third anniversaries of the date of grant.  The date of grant was March 13, 2008.</footnote>
        <footnote id="F7">Information with respect to this grant was inadvertently omitted from the original Form 3 filing due to an administrative error.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Jennifer L. Kraft - by Jennifer L. Kraft pursuant to a power of attorney from Kathryn Hayley</signatureName>
        <signatureDate>2008-08-11</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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