Kingstree is a city and the county seat of Williamsburg County, South Carolina, United States. The population was 3,328 at the 2010 censu…Kingstree is a city and the county seat of Williamsburg County, South Carolina, United States. The population was 3,328 at the 2010 census. The original town was laid out as Williamsburg by the Lords Proprietors in colonial times, but a lone, unusually large white pine was found along the Black River. Since tall white pines were ideal for use as masts for ships, it was claimed by the Crown on behalf of the king. The broad arrow mark was carved into the tree to prevent any colonists from cutting it. Though white pines are native to the Appalachians as far south as Georgia, it is the only tree of King George’s ever found in the South. Over time, the county kept the name Williamsburg, but the county seat became known as the King's Tree.