There are 7 US Post Offices in Jersey County serving a total of 25,147 residents equating to 3,592 residents per post office. It's estimated that approximately 40,137 packages are handled across the 7 county post offices annually. Jersey County is a county located in the U.S. state of Illinois. According to the 2010 census, it has a population of 22,985. The county seat is Jerseyville. Jersey County is included in the St. Louis, MO-IL Metropolitan Statistical Area."