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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-05-04</periodOfReport>

    <issuer>
        <issuerCik>0000097216</issuerCik>
        <issuerName>TEREX CORP</issuerName>
        <issuerTradingSymbol>TEX</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001193675</rptOwnerCik>
            <rptOwnerName>CHOLMONDELEY PAULA H</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>200 NYALA FARM ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2009-05-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>S</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>175</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>15.37</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>12641</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Proceeds from the sale will be used by the reporting person to purchase shares in the Issuer in a retirement plan for the benefit of the reporting person. The sale transaction and future purchase transaction will be matchable under Section 16(b) of the Securities Exchange Act of 1934. The reporting person has agreed to pay to the Issuer the full amount of any profit realized in connection with such short-swing transactions, less transaction costs.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Scott J. Posner, by Power of Attorney</signatureName>
        <signatureDate>2009-05-06</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0303
4
2009-05-04
0000097216
TEREX CORP
TEX
0001193675
CHOLMONDELEY PAULA H
C/O TEREX CORPORATION
200 NYALA FARM ROAD
WESPORT
CT
06880
1
0
0
0
Common Stock, par value $.01
2009-05-04
4
S
0
175
15.37
D
12641
D
Proceeds from the sale will be used by the reporting person to purchase shares in the Issuer in a retirement plan for the benefit of the reporting person. The sale transaction and future purchase transaction will be matchable under Section 16(b) of the Securities Exchange Act of 1934. The reporting person has agreed to pay to the Issuer the full amount of any profit realized in connection with such short-swing transactions, less transaction costs.
/s/ Scott J. Posner, by Power of Attorney
2009-05-06