There are 10 US Post Offices in Canyon County serving a total of 122,296 residents equating to 12,230 residents per post office. It's estimated that approximately 195,198 packages are handled across the 10 county post offices annually. Canyon County is a county located in the U.S. state of Idaho. As of the 2010 census, the population was 188,923, making it the second-most populous county in Idaho. The county seat is Caldwell, and its largest city is Nampa. Canyon County is part of the Boise, ID Metropolitan Statistical Area."