Looks like that rumored image we ran last night of the protagonist from Assassin's Creed III checks out—Ubisoft has posted the official box art from the game to Facebook that depicts the same tomahawk-wielding gentleman. In addition, Game Informer has shared the art from their cover story on the game, further confirming the setting.
Looks like Assassin's Creed is indeed going to take place during the American Revolutionary War.
Here's our own Luke Plunkett with an in-depth look at why a colonial Assassin's Creed makes complete sense (and sounds awesome). He's got me convinced.