There are 20 US Post Offices in Peoria County serving a total of 111,932 residents equating to 5,597 residents per post office. It's estimated that approximately 178,656 packages are handled across the 20 county post offices annually. Peoria County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 186,494. Its county seat is Peoria. Peoria County is part of the Peoria, IL Metropolitan Statistical Area."