There are 8 US Post Offices in Fayette County serving a total of 21,965 residents equating to 2,746 residents per post office. It's estimated that approximately 35,059 packages are handled across the 8 county post offices annually. Fayette County is a county located in the U.S. state of Illinois. As of the 2010 census, the population was 22,140. Its county seat is Vandalia. Ramsey Lake State Recreation Area is located in the northwest part of this county."