Stillwater is a city in north-central Oklahoma at the intersection of U.S. 177 and State Highway 51. It is the county seat of Payne County, Oklahoma, United States. As of the 2010 census, the city population was 45,688. Stillwater is the principal city of the Stillwater Micropolitan Statistical Area which had a population of 77,350 according to the 2010 census. Stillwater was part of first Land Run held April 22, 1889, when Oklahoma Territory's Unassigned Lands were opened for settlement.