Dayton (/ˈdeɪtən/; local pronunciation: /ˈdeɪʔn/) is the sixth-largest city in the U.S. state of Ohio and is the county seat of Montgomery County. A small portion of the city extends into Greene County. In the 2010 census, the population was 141,527, and the Dayton metropolitan area had 799,232 residents, making it Ohio's fourth-largest metropolitan area, after Cleveland, Cincinnati, and Columbus and the 63rd-largest in the United States. The Dayton-Springfield-Greenville Combined Statistical Area had a population of 1,080,044 in 2010, making it the 43rd-largest in the United States. Dayton is within Ohio's Miami Valley region, just north of the Cincinnati–Northern Kentucky metropolitan area.

Ohio's borders are within 500 miles (800 km) of roughly 60 percent of the country's population and manufacturing infrastructure, making the Dayton area a logistical centroid for manufacturers, suppliers, and shippers. Dayton also hosts significant research and development in fields like industrial, aeronautical, and astronautical engineering that have led to many technological innovations. Much of this innovation is due in part to Wright-Patterson Air Force Base and its place within the community. With the decline of heavy manufacturing, Dayton's businesses have diversified into a service economy that includes insurance and legal sectors as well as healthcare and government sectors.

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