There are 3 US Post Offices in Power County serving a total of 7,042 residents equating to 2,347 residents per post office. It's estimated that approximately 11,240 packages are handled across the 3 county post offices annually. Power County is a county located in the U.S. state of Idaho. As of the 2010 Census, the county had a population of 7,817. The county seat and largest city is American Falls. The county was created by the Idaho Legislature on January 30, 1913, by a partition of Cassia County. It is named for an early hydroelectric power plant (1902) at the American Falls."