Stillwater is the tenth-largest city in the U.S. state of Oklahoma. It is the county seat of Payne County, Oklahoma. It is located in north-central Oklahoma at the intersection of U.S. Route 177 and State Highway 51. As of the 2020 census, the city population was 48,394. The Stillwater Micropolitan Statistical Area had a population of 78,399 according to the 2012 census estimate.