Frohn Township is in southern Beltrami County. The Mississippi River runs through it, and most of Wolf Lake is in the township. Frohn Township is bounded on the west by Bemidji Township and the City of Bemidji, on the west by Ten Lake Township, on the north by Turtle River Township, and on the south by the Hubbard County line. The unincorporated village of Rosby is in the southwestern part of the township.