There are 6 US Post Offices in Posey County serving a total of 22,813 residents equating to 3,802 residents per post office. It's estimated that approximately 36,412 packages are handled across the 6 county post offices annually. Posey County is a county located in the southwestern corner of the U.S. state of Indiana. As of 2010, the population was 25,910. The county seat is Mount Vernon. Posey County is part of the Evansville, IN\u2013KY Metropolitan Statistical Area."