The Teton River headwaters are in the southern Lewis Range of the Rocky Mountains at the continental divide, in the Lewis and Clark National Forest.

It flows southeast, then east, down from the Lewis mountains and across Teton County, past the town of Choteau.

It continues flowing east, passing near Fort Benton to its confluence with the Marias River.

This occurs only 3 miles (4.8 km) upstream of the Marias' confluence with the Missouri River.

This article related to a river in Montana is a stub.