Mills is shown the door; League II.
The Bantams claimed a 2-0 win at Bootham Crescent thanks to second-half goals by James Hanson and Garry Thompson, with the result enough to draw the curtain on Mills' time at the club.
York have only claimed six out of a possible 33 points and directors announced they had terminated Mills' contract with immediate effect after the match.
Gillingham remain at the top of League Two even though they were unable to beat lowly Aldershot.
The Gills came from behind to draw 1-1 after Craig Reid put Aldershot in front just after the break.
Leon Legge headed the equaliser for the visitors in the 75th minute to give them a three-point lead at the top over Port Vale, who dropped points themselves after they were beaten 2-1 by Oxford United.
Third-placed Burton Albion crashed to a 3-0 defeat by Bristol Rovers, while Exeter's 3-0 win over Northampton saw them close the gap to fourth place to a single point.
Cheltenham remained in the play-offs thanks to a 2-1 win over Wimbledon.
Steve Elliott headed the opener before Darren Carter fired the second, with Brennan Dickenson's goal for Wimbledon not enough to change the outcome of the match.
Morecambe powered past Rochdale with goals from Christopher McCready, Kevin Ellison and Andrew Fleming as they won 3-0. Plymouth claimed a vital 2-1 win over Barnet but stay in the bottom two.
Jake Hyde put Barnet ahead in the 21st minute but Plymouth battled back, with Conor Hourihane levelling the scores at half-time before Ronan Murray fired the winner in the 49th minute.
Southend and Rotherham drew 1-1, Rotherham's Johnny Mullins cancelling out Kevan Hurst's 73rd-minute goal with an equaliser two minutes from full-time.
The match between Accrington and Torquay ended goalless while Anthony Stewart's 90th-minute header saw Wycombe edge past Fleetwood.
Chesterfield also won by a one-goal margin, Abu Ogogo's headed own goal enough to see them beat Dagenham & Redbridge 1-0.