There are 15 US Post Offices in Franklin County serving a total of 40,836 residents equating to 2,722 residents per post office. It's estimated that approximately 65,179 packages are handled across the 15 county post offices annually. Franklin County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 39,561. Its county seat is Benton. It is located in the southern portion of Illinois known locally as \"Little Egypt\"."