Thurston County is a county located in the U.S. state of Washington. It is named after Samuel R. Thurston, the Oregon Territory's first delegate to Congress. As of the 2010 census, its population was 252,264. The county seat is at Olympia, the state capital and also the county's largest city.
Thurston County was created out of Lewis County by the government of Oregon Territory on January 12, 1852. At that time, it covered all of the Puget Sound region and the Olympic Peninsula. On December 22 of the same year, Pierce, King, Island, and Jefferson Counties were split off from Thurston County.