Fergus County is a county in the U.S. state of Montana. As of the 2020 census, the population was 11,446. Its county seat is Lewistown. The county was founded in 1885 and named for James Fergus, a Montana politician who was instrumental in creating the county.

Lewistown is a city in and the county seat of Fergus County, Montana, United States. The population was 5,952 at the 2020 census. Lewistown is located in the geographic center of the state, southeast of Great Falls and northwest of Billings. First planned in 1882, it was the site of an 1880s gold rush, and served as an important railway destination, supplying surrounding communities with bricks via rail.