But he failed to prevent relegation to the bottom tier of League football, and Saturday's humiliating 5-1 defeat at Rushden and Diamonds was the final straw for the club's board.
After that match, Mills had refused to walk away from the job and launched an ill-advised attack at the club's fans.
Veteran player Ian Richardson will act as caretaker player-manager.
Mills becomes the 12th Football League manager to lose his job this season.
List in full:
Aug 6 - Mark Wright (Chester)
Aug 23 - Paul Sturrock (Southampton)
Aug 29 - Craig Brown (Preston)
Aug 30 - Sir Bobby Robson (Newcastle)
Sept 6 - Graeme Souness (Blackburn)
Sept 18 - Chris Turner (Sheffield Wednesday)
Oct 11 - Micky Adams (Leicester)
Oct 22 - Jimmy Quinn (Shrewsbury)
Oct 26 - Gary Megson (West Brom)
Oct 28 - Jan Molby (Kidderminster)
Nov 1 - Dave Jones (Wolves)
Nov 4 - Gary Mills (Notts County)