There are 14 US Post Offices in Stephenson County serving a total of 48,854 residents equating to 3,490 residents per post office. It's estimated that approximately 77,976 packages are handled across the 14 county post offices annually. Stephenson County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 47,711. Its county seat is Freeport. Stephenson County is included in the Freeport, IL Micropolitan Statistical Area, which is also included in the Rockford-Freeport-Rochelle, IL Combined Statistical Area."