Ashton joined the Boro back in January 2009 from Grays Athletic, and had been an established member of the squad with 225 appearances in major competitions.
He is one of 13 players who have been let go by Stevenage, who are in talks with Teddy Sheringham for him to become the club’s new manager, with Graham Westley to leave at the end of his contract on May 31.
Striker Chris Beardsley, who enjoyed two spells at Stevenage and clocked nearly 150 appearances, is also on the exit list as is former France Under-21 international Bira Dembele.
Stevenage chairman Phil Wallace said: “We’d like to thank all 13 players for their efforts but in particular Jon Ashton and Chris Beardsley.
“Jon leaves us having made over 220 appearances during a successful six-year spell and stepped forward as skipper last season. Chris was also part of the successful squad that won consecutive promotions and enjoyed success in the FA Cup.
“Both have proved key to Stevenage FC establishing itself as a Football League club under Graham Westley.”
The other players released were Roarie Deacon, Joseph N’Guessan, Fejiri Okenabirhie, George Allen, Sam Beasant, Michael Richens, Harry Worley, Andy Bond, Simon Walton and Calvin Zola.