Valley County is a rural county located in the U.S. state of Idaho. As of the 2020 census, the population was 11,746. The county seat is Cascade, and the largest city is McCall. Established in 1917, it was named after the Long Valley of the North Fork of the Payette River, which extends over 30 miles from Payette Lake at McCall south to Cascade to Round Valley. The valley was formerly a summer pasture for livestock from the Boise Valley.