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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-08-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000101199</issuerCik>
        <issuerName>UNITED FIRE GROUP INC</issuerName>
        <issuerTradingSymbol>UFCS</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001515002</rptOwnerCik>
            <rptOwnerName>Sheeley Michael J.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52401</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>VP/COO - United Life Ins. Co.</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-08-05</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>34.79</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5534</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through routine payroll deduction and participation in Issuer's Employee Stock Purchase Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the administrator of the Issuer's Employee Stock Purchase Plan for the Reporting Person, based on astatement of the administrator.</footnote>
        <footnote id="F3">The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,311 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; and 1,439 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Michael J. Sheeley by Michael T. Wilkins, Attorney-in-Fact</signatureName>
        <signatureDate>2015-08-05</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-08-05
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001515002
Sheeley Michael J.
118 SECOND AVENUE SE
CEDAR RAPIDS
IA
52401
0
1
0
0
VP/COO - United Life Ins. Co.
Common Stock
2015-08-05
4
J
0
1
34.79
A
5534
D
Shares acquired through routine payroll deduction and participation in Issuer's Employee Stock Purchase Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the administrator of the Issuer's Employee Stock Purchase Plan for the Reporting Person, based on astatement of the administrator.
The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,311 shares held directly by Mr. Sheeley; 1,033 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/15/2018; 1,710 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/21/2019; and 1,439 shares of restricted stock issued under the Issuer's Stock Plan which vest, subject to certain conditions, on 02/20/2020.
/s/ Michael J. Sheeley by Michael T. Wilkins, Attorney-in-Fact
2015-08-05