There are 4 US Post Offices in Valley County serving a total of 9,971 residents equating to 2,493 residents per post office. It's estimated that approximately 15,915 packages are handled across the 4 county post offices annually. Valley County is a rural county located in the U.S. state of Idaho. As of the 2010 census, the population was 9,862. 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 (50 km) from Payette Lake at McCall south to Cascade to Round Valley. The valley was formerly a summer pasture for livestock from the Boise Valley. Since the completion of the Cascade Dam in 1948, much of the northern valley has been covered by the Cascade Reservoir. Valley County is home to the Idaho ground squirrel."