Dayton ( (listen)) is the sixth-largest city in the U.S. 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. 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. Hospitals in the Greater Dayton area have an estimated combined employment of nearly 32,000 and a yearly economic impact of $6.8 billion. It is estimated that Premier Health Partners, a hospital network, contributes more than $2 billion a year to the region through operating, employment, and capital expenditures. In 2011, Dayton was rated the #3 city in the nation by HealthGrades for excellence in healthcare.

Dayton is also noted for its association with aviation; the city is the birthplace of Orville Wright. Other well-known individuals born in the city include poet Paul Laurence Dunbar and entrepreneur John H. Patterson. Dayton is also known for its many patents, inventions, and inventors, most notably the Wright brothers' invention of powered flight. In 2007 Dayton was a part of the top 100 cities in America. In 2008, 2009, and 2010, Site Selection magazine ranked Dayton the #1 mid-sized metropolitan area in the nation for economic development. Also in 2010, Dayton was named one of the best places in the United States for college graduates to find a job.