Dayton ( (listen)) is the sixth-largest city in the state of Ohio and the county seat of Montgomery County. A small part of the city extends into Greene County. The 2020 U.S. census estimate put the city population at 137,644, while Greater Dayton was estimated to be at 814,049 residents. The Combined Statistical Area (CSA) was 1,086,512. This makes Dayton the fourth-largest metropolitan area in Ohio and 73rd in the United States. Dayton is within Ohio's Miami Valley region, 50 miles (80 km) north of the Greater Cincinnati 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.