Founded in 1907, Hardin is the youngest and largest town in Big Horn County and serves as the county seat. The town site was purchased from the Lincoln Land Company of Lincoln, Nebraska. C. H. Morill, president of the company, named the new town Hardin in honor of his long term friend, Samuel H. Hardin, cattleman who came to this territory from Texas.

Big Horn County was established on January 13, 1913. The county is 5,025 square miles, equaling 3,250,000 acres, and includes the Crow and Northern Cheyenne Indian Reservations. The courthouse was built in 1937 with the help of the WPA (Works Progress Administration). The rock for the courthouse was quarried from Lime Kiln near Fort Smith, MT.