Musselshell County was created February 2, 1911, by Governor Norris from portions of Fergus County north of the Musselshell River, portions of Yellowstone County south of the river and portions of Meagher County to the west. The name Musselshell comes from the mussel shells found in the river of which Lewis and Clark are credited with naming. Located in South Central Montana, Musselshell County is north of Montana’s most populated county, Yellowstone and south of Petroleum and Fergus Counties. In 1915, Golden Valley County was formed from a western portion of Musselshell County.  To the east, a portion of the border between Musselshell and Rosebud County is the northward sweep of the Musselshell River. 

The town of Roundup, whose name comes from cattle roundups of the late 1800’s and first established in 1908, is the county seat.  Roundup provides all services plus a local hospital and houses a Class B school. 

Coal mines began producing in 1908 and dwindled after 1956 with the last major mine closing in 1959. Mom and pop mines provided local coal for years. An underground mine south of Roundup struggled to resurge in the 1990’s, but finally grew back to full production in 2009 as the Signal Peak Mine with over 300 employees. 

Regardless of economic boom or bust, Musselshell County is a resilient and cyclical place. The Flood of 2011, described as a 100 year flood, the Fires of 2012 and another flood in 2013 have changed the face of the County physically. However, the people remain steadfast working with local government and industry helping one another to produce major rebuilding of roads, bridges and homes.