The Teton River (pronounced "TEE-tuhn") is a tributary of the Marias River, approximately 150 mi (241 km) long, in northwestern Montana in the United States. It rises in the Lewis and Clark National Forest, in the southern Lewis Range of the Rocky Mountains at the continental divide. It flows southeast, then east, down from the mountains and across Teton County, past Choteau, and is joined by Muddy Creek and Deep Creek. It flows east, passing near Fort Benton and joins the Marias only 3 mi (5 km) upstream of the confluence of the Marias and the Missouri.