The 25-year-old former Everton man carried on his superb form from late last season with six goals in five games, including a hat-trick in the 5-1 win over Bournemouth.
Huddersfield manager Mark Robins said: "This award caps a superb month for James who is a top class, all-round performer and as good a striker as you could want in the Sky Bet Championship.
"He possesses genuine pace and great movement. He's strong, brave, good in the air and has a tireless work ethic. Most importantly for us, he's a great finisher - he puts the ball in the net."