The Utah and Northern Railway reached Beaver Canyon in 1879.

[7] By the 1900 Census, 1,199 residents lived in the five precincts of Birch Creek, Dubois, Kilgore, Medicine Lodge, and Spencer.

[11][12] It was named for state senator Sam K. Clark, an early pioneer on Medicine Lodge Creek in the upper Snake River valley.

[15] The northern border of the county is the Bitterroot Range of the Rocky Mountains, which forms the state line with Montana and is also the continental divide.

It is crossed by Interstate 15 over Monida Pass at 6,820 feet (2,080 m) above sea level.

As of the 2010 census, there were 982 people, 345 households, and 243 families living in the county.

There were 531 housing units at an average density of 0.3 per square mile (0.12/km2).

[24] As of the 2000 census, there were 1,022 people, 340 households, and 257 families living in the county.

20.00% of all households were made up of individuals, and 8.50% had someone living alone who was 65 years of age or older.

Clark County High School competes in athletics in the Rocky Mountain Conference in IHSAA 1A Division II; the school colors are orange and black and its mascot is a bobcat.

It is represented in the United States Senate by Republicans Mike Crapo and James Risch.

Other officials include sheriff, county clerk, attorney, coroner, treasurer, and assessor.