The 28-year-old, who recently returned to the squad after more than a year out with a knee injury, has been handed a one-year extension.
Cohen has proven himself a popular and versatile figure since arriving at The City Ground from Yeovil in 2007 and the former club captain can now focus on trying to reestablish himself in Forest's starting line-up.
He told nottinghamforest.co.uk: "I’m delighted. As predictable as it may sound, since I first started playing football I always wanted to stay at a club for ten years. I wanted to have a testimonial somewhere.
"Having been at West Ham as a kid, I thought I might do it there but obviously things didn’t work out. As much as I loved my time at Yeovil, the club’s aspirations didn’t match my own. Then I signed for a wonderful, wonderful football club.
"It’s been a crazy journey. We've come so close to the Premier League a couple of times and I've had to come back from injuries. The amount of support I’ve had from the club, the chairman especially, has made me desperate to stay.
"As I'm sure the club will agree, these negotiations were very easy. I came on my own to one meeting with a realistic idea of what I wanted. I've been very injury prone over the years so the terms of the deal are more based on me playing football, which is only right.
"It’s not a sympathy year from the club. The chairman and manager see me as being a part of the team, which is important for me. I’m here to play games.
"I feel like I’m training really well, getting stronger every week and I’m waiting for my opportunity, after the boys have been doing so well, to get back into the team.
"I really couldn’t be happier and tonight I’ll celebrate with my wife and little boy."