Mills has brought in 20-year-old Leicester City striker Ashley Chambers together with left-sided Sunderland midfielder Robbie Weir.
Chambers is a former England Under-19 international and originally made his Foxes debut as a fifteen-year-old.
He spent time on loan at both Wycombe Wanderers and Grimsby Town last season and has signed for the Minstermen until January.
Meanwhile, Weir was a regular for the Black Cats' reserve side last season and is a Northern Ireland Under-21 international.
The 21-year-old impressed for York's reserves during a trial match earlier this week and has joined them for a month.
Both will go into the squad for the visit of Wrexham to Bootham Crescent this weekend, subject to FA clearance.
However, York will be without skipper Chris Smith for the game as he serves a one-match ban after collecting his fifth caution of the season at Rotherham last week.
York City have boosted their squad with the loan signings of Leicester City's former England Under-19 striker Ashley Chambers (top right) and Sunderland's Northern Ireland Under-21 international midfielder Robbie Weir (below).