The seat of Musselshell County
, Roundup is found 50 miles north of Billings
on US 87/US 12, near Lake Mason National Wildlife Refuge. Once a gathering point for large herds of cattle that grazed up and down the valley, Roundup is located on the Musselshell River
near the Bull Mountains. The Musselshell Valley Historical Museum includes a pioneer-era cabin, 5-room house, coal mine and 7,000-sq. ft. exhibit area.