The Minstermen have shipped 28 goals in 17 League Two games this season, to sit third-from-bottom and just two points off the relegation zone.
New York manager Jackie McNamara saw Town’s Under-21 captain in action against Leeds United Under-21s on Monday, and the 20-year-old centre-half impressed.
Boyle – who has been a Town substitute several times this season – has signed on a youth loan with York until January 3.
It will be his third loan move, after spells at non-league Kidderminster Harriers and Macclesfield Town, but his first in the Football League.
“York manager Jackie McNamara approached the club about William’s availability straight after watching him in action first-hand in the 2-0 Under-21 win at Leeds United on Monday,” said Town’s senior professional development coach Frankie Bunn.
“This will be William’s third spell and now is the time for him to go and establish himself in York’s side, which we all believe he is more than capable of doing.
“He’s a great character – a leader on the pitch – and this is potentially a superb next step in his development as a footballer.”
Boyle is set to make his debut at Leyton Orient on Saturday.
Kieran Wallace hopes the security of a new long-term deal at Sheffield United can help bring out his best on the pitch.
The 20-year-old, who arrived from non-league Ilkeston Town 12 months ago, has signed a contract until the summer of 2018.
Blades boss Nigel Adkins said he wanted to give the utility player more ‘security and stability’ to help aid his development.
Having chalked up 15 appearances for the Blades this season, that extra security is a huge bonus for Wallace.
He said: “For the first time in my career I have been given a contract that means I focus all my attentions into my game rather than worrying about the future.
“I have exceeded my own expectations in terms of how much I have played.
“But I want to keep learning and developing, I want to keep taking my chances when they come and hopefully now I pay back the club and the gaffer for the trust and commitment they have shown in giving me this contract.”