Washington County is a county located in the U.S. state of Georgia. As of the 2010 census, the population was 21,187. The county seat is Sandersville. The county was established on February 25, 1784. It was named for Revolutionary War general (and afterward President of the United States) George Washington.
According to the U.S. Census Bureau, the county has a total area of 684 square miles (1,770 km2), of which 678 square miles (1,760 km2) is land and 5.9 square miles (15 km2) (0.9%) is water.
The western portion of Washington County, west of a north-to-south line running through Sandersville, is located in the Lower Oconee River sub-basin of the Altamaha River basin. The northeastern portion of the county, north of Riddleville, is located in the Upper Ogeechee River sub-basin of the Ogeechee River basin, while the southeastern portion, centered on Harrison, is located in the Ohoopee River sub-basin of the Altamaha River basin.