There are 5 US Post Offices in Marion County serving a total of 30,650 residents equating to 6,130 residents per post office. It's estimated that approximately 48,921 packages are handled across the 5 county post offices annually. Marion County is a county located in the U.S. state of South Carolina. As of the 2010 census, its population was 33,062. Its county seat is Marion. The county was created in 1785 and was originally known as Liberty County. However, four years later it was renamed Marion County, in honor Brigadier General Francis Marion, the famous \"Swamp Fox\" and a hero of the American Revolutionary War."