Turnbull made his Stockport debut as a 16-year-old
Northampton Town have signed Stockport County midfielder Paul Turnbull for an undisclosed compensation fee.
The 22-year-old made 45 appearances for the Hatters last season, scoring five goals as they were relegated to the Blue Square Bet Premier.
"I've had ten years at Stockport and I needed a change to move on with my career," Turnbull told BBC Radio Northampton.
"I wanted to stay in the Football League so it was hard to turn down."
Former trainee Turnbull was the captain and longest-serving player at Edgeley Park, having made 152 appearances since making his debut in April 2005.
"The manager has said that he wants a team full of leaders, with players who can push on for promotion," he said.
He was offered a new one-year deal at Edgeley Park, but rejected terms to make the move to Sixfields.
"I think Paul is another very good signing for this football club, both now and for the future," said boss Gary Johnson.
"There aren't many 22-year-old central midfield players who have captained their club and made more than 100 appearances in senior football.
"He is a leader, a player who controls things from central midfield, and someone who I, and many others, feel he has great potential.
"He can be a defensive midfielder and can also be an attacking midfielder, he has both types of game in his locker and that is important.
"There was a fair bit of interest in him this summer, including from clubs in higher divisions, so we have done well to bring him to Sixfields."