There are 19 US Post Offices in Richland County serving a total of 393,735 residents equating to 20,723 residents per post office. It's estimated that approximately 628,445 packages are handled across the 19 county post offices annually. Richland County is a county located in the U.S. state of South Carolina. As of the 2010 census, the population was 384,504, making it the second-most populous county in South Carolina, behind only Greenville County. The county seat is Columbia, the state capital. Richland County is part of the Columbia, SC Metropolitan Statistical Area. In 2010, the center of population of South Carolina was located in Richland County, in the city of Columbia."