The Gallatin Pioneer Museum (317 W. Main St., 406/522-8122, www.pioneermuseum.org , 10 a.m.–5 p.m. Mon.–Sat. Memorial Day–Labor Day, 11 a.m.–4 p.m. Tues.–Sat. Labor Day–Memorial Day, $5, children 12 and under and museum members, free) took over the old county jail in 1982; there are still jail cells and a gallows among the Indian artifacts, old household items, and barbed wire collections.
Other exhibits feature the story of John Bozeman, a mountain man and immigrant guide of the 1860s; his namesake trail, essentially a spur of the Oregon Trail leading to Montana’s gold country, ran along what is now a section of I-90. Frequent attacks by Sioux and Cheyenne bands plagued sojourners on the Bozeman Trail. Bozeman was killed, perhaps by Blackfeet (or perhaps by a business colleague or a jealous husband), near Livingston  in 1867.
Largely as a reaction to John Bozeman’s murder, Fort Ellis was established in 1867 at the site where William Clark and his party camped on July 14, 1806. It was the supply post for the U.S. Army cavalry during the Battle of the Little Bighorn in 1876 and provided military escort for railroad surveyors in the 1880s.
The fort itself no longer stands, but local guys with metal detectors have turned up relics that are incorporated into a model at the museum.