<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2005-01-11</periodOfReport>

    <dateOfOriginalSubmission>2005-03-16</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001016152</issuerCik>
        <issuerName>CORNELL COMPANIES INC</issuerName>
        <issuerTradingSymbol>CRN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001316405</rptOwnerCik>
            <rptOwnerName>Hyman James E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1700 WEST LOOP SOUTH, SUITE 1500</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>HOUSTON</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>77027</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman, CEO and President</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>25000</value>
                    <footnoteId id="F1"/>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">These shares were previously reported as 85,000 shares in the reporting person's original Form 3.  However, there were 60,000 performance-based restricted shares that should not have been reported in the original Form 3 and therefore have been removed and are not reflected in this amended Form 3.  Such performance-based shares were subsequently cancelled on August 2, 2007.</footnote>
        <footnote id="F2">The date of the event requiring the statement in the reporting person's original Form 3 was reported as March 14, 2005, the date of the reporting person's employment agreement with the issuer.  However, the reporting person was appointed to the board of directors of the issuer on January 11, 2005.  Therefore, the date of the event requiring the statement has been changed to reflect the date the reporting person was appointed to the board of directors of the issuer.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>William Turcotte, by Power of Attorney</signatureName>
        <signatureDate>2008-03-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
