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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2014-12-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001203171</rptOwnerCik>
            <rptOwnerName>RIFE JOHN A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>118 SECOND AVENUE SE</rptOwnerStreet1>
            <rptOwnerStreet2>P.O. BOX 73909</rptOwnerStreet2>
            <rptOwnerCity>CEDAR RAPIDS</rptOwnerCity>
            <rptOwnerState>IA</rptOwnerState>
            <rptOwnerZipCode>52407-3909</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2014-12-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value>E</value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>59</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>28.05</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>8392</value>
                    <footnoteId id="F3"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See footnote #1</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F2">Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.</footnote>
        <footnote id="F3">The number of shares (excluding frationals) beneficially held indirectly by the Reporting Person includes: 6,591 shares held in an individual retirement account for Mr. Rife's benefit; 1,370 shares held individually by Mr. Rife's spouse; and 431 shares held in a SEP individual retirement account for Mr. Rife's benefit.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ John A. Rife by Barrie W. Ernst, Attorney-in-Fact</signatureName>
        <signatureDate>2014-12-19</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2014-12-15
0
0000101199
UNITED FIRE GROUP INC
UFCS
0001203171
RIFE JOHN A
118 SECOND AVENUE SE
P.O. BOX 73909
CEDAR RAPIDS
IA
52407-3909
1
0
0
0
Common Stock
2014-12-15
5
J
0
E
59
28.05
A
8392
I
See footnote #1
Shares acquired through participation in the Issuer's Dividend Reinvestment Plan.
Represents the approximate number of shares (excluding fractionals) acquired by the Reporting Person through the Issuer's Dividend Reinvestment Plan.
The number of shares (excluding frationals) beneficially held indirectly by the Reporting Person includes: 6,591 shares held in an individual retirement account for Mr. Rife's benefit; 1,370 shares held individually by Mr. Rife's spouse; and 431 shares held in a SEP individual retirement account for Mr. Rife's benefit.
/s/ John A. Rife by Barrie W. Ernst, Attorney-in-Fact
2014-12-19