The following are all attendances over 40,000 at The City Ground. (Current capacity = 30,445)

DateAttendance Game Round Opponent H/A Score Result
Sat Oct 28, 196749,946League Tier 1Manchester UnitedH3-1Win
Sat Oct 12, 195747,804League Tier 1Manchester UnitedH1-2Loss
Sat Apr 08, 196747,510FA CupQuarterEvertonH3-2Win
Mon Dec 26, 197747,218League Tier 1LiverpoolH1-1Draw
Sat Feb 25, 196747,188League Tier 1Leicester CityH1-0Win
Wed Jan 29, 195846,455FA Cup4West Bromwich AlbionH1-5Loss
Sat Jan 27, 196246,218FA Cup4Sheffield WednesdayH0-2Loss
Sat Feb 18, 196745,962FA Cup4Newcastle UnitedH3-0Win
Sat Mar 11, 196745,898FA Cup5Swindon TownH0-0Draw
Wed Aug 27, 195844,971League Tier 1Manchester UnitedH0-3Loss
Tue Aug 22, 196744,950League Tier 1Coventry CityH3-3Draw
Sat Feb 28, 195944,414FA CupQuarterBolton WanderersH2-1Win
Sat Mar 01, 193044,166FA CupQuarterSheffield WednesdayH2-2Draw
Mon Jan 02, 197844,030League Tier 1EvertonH1-1Draw
Sat Jan 14, 196743,849League Tier 1Leeds UnitedH1-0Win
Sat Jan 16, 196543,009League Tier 1Manchester UnitedH2-2Draw
Mon Dec 27, 197142,750League Tier 1ArsenalH1-1Draw
Sat Jan 24, 195942,362FA Cup3Tooting and Mitcham UnitedH3-0Win
Tue Apr 19, 196042,335League Tier 1Wolverhampton WanderersH0-0Draw
Sat Mar 14, 197042,074League Tier 1Derby CountyH1-3Loss
Sat Dec 26, 196442,056League Tier 1Tottenham HotspurH1-2Loss
Sat Apr 28, 197941,898League Tier 1LiverpoolH0-0Draw
Mon Mar 31, 196941,892League Tier 1Manchester UnitedH0-1Loss
Sat Oct 01, 196641,854League Tier 1Manchester UnitedH4-1Win
Sat Sep 28, 195741,825League Tier 1West Bromwich AlbionH0-2Loss
Sat Feb 04, 196741,822League Tier 1Tottenham HotspurH1-1Draw
Sat Oct 26, 195741,586League Tier 1BlackpoolH1-2Loss
Mon Mar 27, 196741,586League Tier 1BurnleyH4-1Win
Sun Jan 27, 197441,472FA Cup4Manchester CityH4-1Win
Sat Apr 15, 196741,468League Tier 1Aston VillaH3-0Win
Sat Oct 19, 196341,426League Tier 1Manchester UnitedH1-2Loss
Sat Aug 19, 197841,223League Tier 1Tottenham HotspurH1-1Draw
Sat Sep 23, 196140,875League Tier 1Tottenham HotspurH2-0Win
Wed Apr 11, 197940,804European CupSemiCologneH3-3Draw
Tue Apr 13, 197140,692League Tier 1ArsenalH0-3Loss
Tue Sep 01, 196440,382League Tier 1EvertonH3-1Win
Sat Mar 15, 195840,197League Tier 1Wolverhampton WanderersH1-4Loss
Mon Feb 27, 197840,097FA Cup5Queens Park RangersH1-1Draw
Sat Dec 27, 195840,057League Tier 1Newcastle UnitedH3-0Win
Sat Jan 19, 195240,005League Tier 2Notts CountyH3-2Win

The following is the list of each new attendance record at home.
(Note: Even though the game against Derby in 1896 that had 20,000 fans was abandoned, it's included in here because it doesn't affect the progression.
If I ignore it, then the next record breaker would still be the 1899 game against Aston Villa).
DateAttendance Game Round Opponent H/A Score Result
Sat Dec 02, 1871450FriendlyChesterfieldH0-0Draw
Tue Dec 23, 18733,000FriendlyRoyal EngineersH1-2Loss
Tue Feb 10, 18805,500FriendlyScottish CanadianH0-2Loss
Fri Dec 26, 18849,000FriendlyNottsH3-0Win
Sat Oct 30, 188615,000FA Cup1Notts OlympicH3-0Win
Sat Oct 03, 189620,000League Tier 1Derby CountyH1-1Aba
Sat Jan 28, 189932,070FA Cup1Aston VillaH2-1Win
Sat Feb 25, 189933,500FA CupQuarterSheffield UnitedH0-1Loss
Tue Dec 26, 191135,000League Tier 2Derby CountyH1-3Loss
Wed Feb 01, 192835,625FA Cup4Derby CountyH2-0Win
Sat Mar 01, 193044,166FA CupQuarterSheffield WednesdayH2-2Draw
Sat Oct 12, 195747,804League Tier 1Manchester UnitedH1-2Loss
Sat Oct 28, 196749,946League Tier 1Manchester UnitedH3-1Win

The following are all attendances under 4,000 at The City Ground since the end of the First World War.
DateAttendance Game Round Opponent H/A Score Result
Tue Oct 31, 20062,031EFL Trophy2BrentfordH2-1Win
Thu Mar 29, 19282,572League Tier 2ReadingH5-3Win
Tue Sep 04, 20073,102EFL Trophy1Peterborough UnitedH2-3Loss
Sat Apr 25, 19313,342League Tier 2Charlton AthleticH4-3Win
Sat Sep 19, 19253,460League Tier 2Wolverhampton WanderersH1-4Loss
Sat Feb 28, 19313,565League Tier 2Cardiff CityH3-1Win
Tue Nov 15, 19603,686League Cup3Bristol CityH2-1Win
Thu Apr 26, 19283,713League Tier 2Port ValeH0-2Loss
Sat Jan 03, 19313,819League Tier 2Bradford Park AvenueH1-0Win
Wed Sep 17, 19303,824League Tier 2BurnleyH3-3Draw
Sat May 06, 19333,842League Tier 2FulhamH1-0Win
Sat May 04, 19353,931League Tier 2Bradford CityH2-0Win
Wed Feb 03, 19374,000League Tier 2Plymouth ArgyleH2-3Loss
Fri Oct 03, 19194,000League Tier 2BlackpoolH2-0Win