There are 6 US Post Offices in Clarendon County serving a total of 32,380 residents equating to 5,397 residents per post office. It's estimated that approximately 51,682 packages are handled across the 6 county post offices annually. Clarendon County is a county located above the fall line in the Coastal Plain region of U.S. state of South Carolina. As of the 2010 census, its population was 34,971. Its county seat is Manning. This area was developed for lumber and mills, including textile mills. Clarendon County boasts one of the largest man-made lakes in the United States, Lake Marion, completed in 1941 as a New Deal project. It was planned as part of a national rural electrification initiative. Since the late 20th century, the dam's generation of hydroelectric power has also stimulated economic development and industry in the region. The South Carolina state legislature, dominated by white Democrats, established racial segregation of public facilities by state law in the late 19th century. During the Civil Rights Movement, Clarendon County was the site of the Briggs v. Elliott trial challenging segregation of public schools. This case was one of five combined with what came to be known as Brown v. Board of Education, under which the United States Supreme Court ruled in 1954 that racial segregation of public schools was unconstitutional."