There are 10 US Post Offices in Calhoun County serving a total of 10,185 residents equating to 1,019 residents per post office. It's estimated that approximately 16,256 packages are handled across the 10 county post offices annually. Calhoun County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 9,670. Its county seat is Rockwell City.