Dayton is a city in Montgomery and Greene counties in the U.S. state of Ohio. As of the 2020 census, the city proper had a population of 137,644, making it the sixth-most populous city in Ohio. It anchors the state's fourth-largest metropolitan area, the Dayton metropolitan area, which had 814,049 residents. Dayton is located within Ohio's Miami Valley region, 50 miles north of Cincinnati and 60 miles west of Columbus. It is the county seat of Montgomery County.