Cohen, 28, only returned to first-team action in January after being sidelined for over a year due to a third serious knee injury.
"I'm delighted," Cohen told the club's official website
"As predictable as it may sound, since I first started playing football I always wanted to stay at a club for 10 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."
Cohen, who joined Forest in 2007, sustained serious cruciate ligament damage for the third time in his career in September 2014 but was back in action in last month and has since made three further appearances.
"It's not a sympathy year from the club," he added
"The chairman and manager see me as being a part of the team, which is important for me
I'm here to play games."
Source : PA