There are 6 US Post Offices in Union County serving a total of 28,039 residents equating to 4,673 residents per post office. It's estimated that approximately 44,753 packages are handled across the 6 county post offices annually. Union County is a county located in the U.S. state of South Carolina. As of the 2010 census, the population was 28,961. Its county seat is Union. The county was created in 1785. Union County is included in the Spartanburg, SC Metropolitan Statistical Area, which is also included in the Greenville\u2013Spartanburg\u2013Anderson, SC Combined Statistical Area."