[2] Established in 1881, the county was named for the General Custer Mine, where gold was discovered five years earlier.

Custer County relies on ranching, mining, and tourism as its main resources.

The Lost River Range, the state's highest mountains, are located in eastern Custer County.

On the western border of the county is Idaho's famous Sawtooth Range; the tallest is Thompson Peak in Custer County, above picturesque Redfish Lake.

Twenty miles (32 km) east are the White Cloud Mountains, the tallest of which is Castle Peak at 11,815 feet (3,601 m).

27.70% of all households were made up of individuals, and 11.30% had someone living alone who was 65 years of age or older.

As of the 2010 United States census, there were 4,368 people, 1,936 households, and 1,244 families living in the county.

The last Democrat to carry the county was John F. Kennedy in 1960, since 1968 no Democrat has passed 37 percent of the county's vote, and the last to pass 28 percent was Michael Dukakis in 1988.

In 2012, the county gave Mitt Romney a first ballot victory in the Republican primary caucus[15] and subsequently voted 74.1 percent for him in the Presidential election.