US 191 in Montana begins at the West Entrance to Yellowstone National Park, at the edge of the town of West Yellowstone. The highway heads north, running concurrently with US 287 for before veering slightly east and entering Yellowstone. US 191 continues northward through Yellowstone, traversing forested, mountainous terrain and briefly looping into the state of Wyoming, before leaving the park in the upper reaches of the Gallatin River canyon. The route travels northward through the narrow canyon, past the resort community of Big Sky, then entering the Gallatin Valley near the town of Gallatin Gateway, Montana. US 191 travels north and east through the valley to the city of Bozeman, which is the largest city along the entire US 191 route.