There are 16 US Post Offices in Mercer County serving a total of 62,035 residents equating to 3,877 residents per post office. It's estimated that approximately 99,015 packages are handled across the 16 county post offices annually. Mercer County is a county located in the U.S. state of West Virginia. At the 2010 census, the population was 62,264. Its county seat is Princeton. The county was originally established in the state of Virginia by act of its General Assembly on 17 March 1837, using lands taken from Giles and Tazewell counties. Mercer County is included in the Bluefield, WV-VA Micropolitan Statistical Area."