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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2007-03-06</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001167145</rptOwnerCik>
            <rptOwnerName>FORD TIMOTHY A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>TEREX CORPORATION</rptOwnerStreet1>
            <rptOwnerStreet2>200 NYALA FARM ROAD</rptOwnerStreet2>
            <rptOwnerCity>WESTPORT</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06880</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>President Terex AWP</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-03-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>5</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>59.51</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>20030</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-03-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8557</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>28587</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-03-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>10502</value>
                    <footnoteId id="F4"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>39089</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock, par value $.01</value>
            </securityTitle>
            <transactionDate>
                <value>2007-03-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>I</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>0</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>35</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>401(k) plan</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Reflects Company match in the Company's Employee Stock Purchase Plan.</footnote>
        <footnote id="F2">Reflects price paid by the Company on January 24, 2007.</footnote>
        <footnote id="F3">Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting as follows: 25% on March 6, 2008; 25% on March 6, 2009; 25% on March 6, 2010; and 25% on March 6, 2011.</footnote>
        <footnote id="F4">Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting if the Company achieves a targeted percentage Return on Invested Capital (&quot;ROIC&quot;) for the four consecutive calendar quarter period ending December 31, 2007.  If this target is achieved, 25% of this grant will vest in the first quarter of 2008, and 25% will vest on each of December 31, 2008, December 31, 2009, and December 31, 2010.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted percentage ROIC measurement.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/  TIMOTHY A. FORD</signatureName>
        <signatureDate>2007-03-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2007-03-06
0000097216
TEREX CORP
TEX
0001167145
FORD TIMOTHY A
TEREX CORPORATION
200 NYALA FARM ROAD
WESTPORT
CT
06880
0
1
0
0
President Terex AWP
Common Stock, par value $.01
2007-03-06
4
P
0
5
59.51
A
20030
D
Common Stock, par value $.01
2007-03-06
4
A
0
8557
0
A
28587
D
Common Stock, par value $.01
2007-03-06
4
A
0
10502
0
A
39089
D
Common Stock, par value $.01
2007-03-06
5
I
0
0
0
A
35
I
401(k) plan
Reflects Company match in the Company's Employee Stock Purchase Plan.
Reflects price paid by the Company on January 24, 2007.
Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting as follows: 25% on March 6, 2008; 25% on March 6, 2009; 25% on March 6, 2010; and 25% on March 6, 2011.
Shares granted pursuant to one of the Company's long-term incentive plans with the award vesting if the Company achieves a targeted percentage Return on Invested Capital ("ROIC") for the four consecutive calendar quarter period ending December 31, 2007.  If this target is achieved, 25% of this grant will vest in the first quarter of 2008, and 25% will vest on each of December 31, 2008, December 31, 2009, and December 31, 2010.  The number of shares in this grant are subject to adjustment, up or down, based upon attainment above or below the targeted percentage ROIC measurement.
/s/  TIMOTHY A. FORD
2007-03-08