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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-02-20</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>2015-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1439</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>29.12</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5483</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Option (right to buy)</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>29.12</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2015-02-20</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8437</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2025-02-20</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>8437.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8437</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.</footnote>
        <footnote id="F2">The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.</footnote>
        <footnote id="F3">The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,301 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>
        <footnote id="F4">Options become vested and exercisable in equal installments on 02/20/2016, 02/20/2017, 02/20/2018, 02/20/2019 and 02/20/2020, respectively.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Michael J. Sheeley by Barrie W. Ernst, Attorney-in-Fact</signatureName>
        <signatureDate>2015-02-23</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-02-20
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
2015-02-20
4
A
0
1439
29.12
A
5483
D
Stock Option (right to buy)
29.12
2015-02-20
4
A
0
8437
0
A
2025-02-20
Common
8437.0
8437
D
This transaction represents a grant of restricted stock shares to the Reporting Person under the Issuer's Stock Plan.
The price per share is the closing price of the Issuer's common stock on the date of the reported transaction.
The total number of securities beneficially held directly by the Reporting Person (excluding fractionals)  includes: 1,301 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.
Options become vested and exercisable in equal installments on 02/20/2016, 02/20/2017, 02/20/2018, 02/20/2019 and 02/20/2020, respectively.
/s/ Michael J. Sheeley by Barrie W. Ernst, Attorney-in-Fact
2015-02-23