The 19-year-old forward has joined Albion on loan from the Championship side until the end of the season.
The England Under-19 international will get to work with Nigel Clough again.
Clough, who was appointed the Albion manager in December, managed Bennett at Derby.
The youngster is delighted to have moved to the League One outfit and hopes to contribute to the team.
Buzzing to be given this opportunity, hopefully carry on the great… https://t.co/DxU3CH1ms0— Mason Bennett (@Masonbennett20) January 15, 2016
"Buzzing to be given this opportunity, hopefully carry on the great form this squad is in!" Bennett added on his Instagram page.
Bennett has not featured for the Derby first team this season, but he has scored four goals in 14 games for their Under-21 side.
Derby are third in the Championship table at the moment with 49 points from 26 matches. The Rams are six points behind leaders Middlesbrough, who have a game in hand.
Meanwhile, Albion currently find themselves at the top of the League One table with 51 points from 24 matches. Clough’s side are a point clear of second-placed Gillingham and have two games in hand.