Thornton, 22, joined the side from Guiseley AFC and has been ever present since his debut against FC United of Manchester in November.
He also scored his first goal for the club in their 5-1 victory over Grantham Town on Boxing Day.
"I am enjoying my time here," he said.
"I am sure the other lads will agree, we are going in the right direction and I want to be a part of this.
"I came in with the manager and really we just all want to get together and get us climbing away from danger and up the league."
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