[4] Musselshell County was created in 1911 by Montana Governor Edwin L. Norris.

That river had been thus named in 1805 by the Lewis and Clark Expedition, due to the abundance of freshwater mussels found along its banks.

The county's northwestern area is rolling grasslands, which slope southeastward to the Musselshell River and the forested Bull Mountains in the southeast.

The county has abundant natural resources of coal deposits, subterranean oil, and timbered slopes.

[citation needed] As of the 2010 census, there were 4,538 people, 2,046 households, and 1,276 families in the county.