There are 12 US Post Offices in Carroll County serving a total of 21,458 residents equating to 1,788 residents per post office. It's estimated that approximately 34,249 packages are handled across the 12 county post offices annually. Carroll County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 20,816. Its county seat is Carroll. The county is named in honor of Charles Carroll of Carrollton, signer of the Declaration of Independence."