The 22-year-old midfielder played on loan for Derby from West Bromwich Albion in 2014.
Then in the summer of 2014, the youngster signed a permanent contract with the Rams.
Explaining his decision to commit his future to the Championship club, Thorne told the Shoot magazine: “I saw the ambition [of the club] when I came on loan.
“The philosophy of the club and the way we play football suits me down to the ground. I believe it will make me a better player. I enjoy playing here and it is important to be enjoying your football.”
Thorne has struggled with injuries since making the move to Derby permanent, but he remains an important player for the Rams.
The midfielder will be looking to play a key role as the season progresses, with Paul Clement’s side aiming to finish in the top two of the Championship this season.
Derby are playing well at the moment and are on a roll, and there is a very good chance that they will gain automatic promotion to the Premier League at the end of the season.
The Rams are fifth in the Championship table at the moment with 30 points from 15 matches, just a point behind leaders Hull City.
Clement’s side will take on Nottingham Forest away from home at the City Ground in the league on Friday evening.