Round O (formerly also called Round) is an unincorporated community in Colleton County, South Carolina, United States. Its elevation is 36 feet (11 m), its ZIP code is 29474, and it is located near the intersection of Cottageville Highway (US 17) and Round O Road (S-15-45). Its geographic coordinates are (32.9371, −80.5409). There are numerous churches within the community, including Canaan Baptist Church and Mount Sinai Baptist. It also has a small US Post Office.
According to tradition, the community received its name from a local Native American who painted his torso with a circular design.