There are 4 US Post Offices in Wabash County serving a total of 11,638 residents equating to 2,910 residents per post office. It's estimated that approximately 18,576 packages are handled across the 4 county post offices annually. Wabash County is a county located in the U.S. state of Illinois. According to the 2010 census, it had a population of 11,947. Its county seat is Mount Carmel. It is located in the southern portion of Illinois known locally as \"Little Egypt\"."