There are 6 US Post Offices in Mccormick County serving a total of 10,032 residents equating to 1,672 residents per post office. It's estimated that approximately 16,012 packages are handled across the 6 county post offices annually. McCormick County is a county located in the U.S. state of South Carolina. As of the 2010 census, its population was 10,233, making it the least-populous county in South Carolina. Its county seat is McCormick. The county was formed in 1916 from parts of Edgefield, Abbeville, and Greenwood Counties."