There are 18 US Post Offices in Harrison County serving a total of 72,696 residents equating to 4,039 residents per post office. It's estimated that approximately 116,031 packages are handled across the 18 county post offices annually. Harrison County is a county in the U.S. state of West Virginia. As of the 2010 census, the population was 69,099. The county seat is Clarksburg. The county was founded in 1784. Harrison County is part of the Clarksburg, WV Micropolitan Statistical Area."