Dayton (/ˈdeɪtən/ ) is a city in Montgomery County, Ohio, United States, and its county seat. It is the sixth-most populous city in Ohio, with a population of 137,644 at the 2020 census. The Dayton metropolitan area has an estimated 822,000 residents and is the state's fourth-largest metropolitan area. Dayton is located within Ohio's Miami Valley region, 50 miles (80 km) north of Cincinnati and 55 miles (89 km) southwest of Columbus.
Dayton was founded in 1796 along the Great Miami River and named after Jonathan Dayton, a Founding Father who owned a significant amount of land in the area. It grew in the 19th century as a canal town and was home to many patents and inventors, most notably the Wright brothers, who developed the first successful motor-operated airplane. It later developed an industrialized economy and was home to the Dayton Project, a branch of the larger Manhattan Project, to develop polonium triggers used in early atomic bombs. With the decline of heavy manufacturing in the late 20th century, Dayton's businesses have diversified into a service economy.