Custer County is a rural mountain county in the center of the U.S. state of Idaho. As of the 2020 census, the population was 4,275, making it the fifth-least populous county in Idaho. The county seat is Challis. 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 Sawtooth Range is a mountain range of the Rocky Mountains in central Idaho, United States, reaching a maximum elevation of 10,751 feet (3,277 m) at the summit of Thompson Peak. It encompasses an area of 678 square miles (1,756 km2) spanning parts of Custer, Boise, Blaine, and Elmore counties, and is bordered to the east by the Sawtooth Valley. Much of the mountain range is within the Sawtooth Wilderness, part of the Sawtooth National Recreation Area and Sawtooth National Forest.