The Gallatin River is a tributary of the Missouri River, approximately 120 mi (193 km long), in the U.S. states of Wyoming and Montana. It is one of three rivers, along with the Jefferson and Madison, that converge near Three Forks, Montana, to form the Missouri. It rises in the northwest corner of Yellowstone National Park, in northwestern Wyoming, in the Gallatin Range of the Rocky Mountains. It flows northwest through Gallatin National Forest, past Big Sky, Montana, and joins the Jefferson and Madison approximately 30 mi (48 km) northwest of Bozeman. U.S. Highway 191 follows the river from the Wyoming border to just outside Bozeman.