Dayton () 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 2019 U.S. census estimate put the city population at 140,407, while Greater Dayton was estimated to be at 803,416 residents. This makes Dayton the fourth-largest metropolitan area in Ohio and 63rd in the United States. Dayton is within Ohio's Miami Valley region, just north of Greater Cincinnati.
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 in 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.
Along with defense and aerospace, healthcare accounts for much of the Dayton area's economy.