From Bozeman, US 191 is concurrent with I-90 eastward to Big Timber, where it proceeds north. The road travels through hilly ranch country near the eastern edge of the Crazy Mountains to Harlowton, where US 191 is briefly concurrent with US 12. North of Harlowton, US 191 is concurrent with Montana Highway 3 for , to Eddie's Corner. US 191 proceeds eastward from Eddie's Corner to Lewistown, on a roadway shared with US 87 and Montana 200, in a wrong-way concurrency.