The 31-year-old made 45 appearances for the Exiles after joining the club last summer but has rejected the offer of a contract extension and has returned to one of his former clubs.
Jones made over 100 appearances for Rovers during a three-year stay between 2006 and 2009.
Newport manager Terry Butcher told the club’s official website: “We tried our best to keep him, and offered him an increased deal, but sadly despite our best efforts we can’t get anywhere near what he has been offered at Forest Green Rovers.
“As many supporters know, Forest Green Rovers, despite being in the Conference, have a history of being able to offer big deals, and it looks as though Darren will now join up with them.
“We wish him well, and we totally understand his decision to move. He had spoken of his wishes to stay at Newport, but obviously he has to put his family first, and the deal he has been offered at Forest Green is unbeatable from our point of view.”
“Darren has been a fantastic servant to the club and I am sure all the supporters will join me in wishing him well for the future.”