Dayton is a city in southwestern Ohio, United States. It is the county seat and largest city of Montgomery County. As of the 2005 census estimate, the population of Dayton was 158,873. The Dayton metropolitan area, or Greater Dayton, which includes the communities of Vandalia, Trotwood, Kettering, Centerville, Beavercreek, West Carrollton, Huber Heights, Troy, and Miamisburg, had a population of 843,577 as of the 2005 estimate. Dayton is situated within the Miami Valley region of Ohio, just north of the Cincinnati metropolitan area. Dayton is located at 39°45′46″N, 83°11′48″W (39.762708, -84.196665). The city sits in the Miami River Valley, north of Cincinnati, well south of Toledo, south-west of Columbus, and east of Richmond, Indiana, in the southwest quadrant of the state. Most official and government designations place it in west-central Ohio (a term which colloquially often refers to Lima, Ohio). It is at the confluence of the Great Miami River, the Stillwater and Mad rivers, and Wolf Creek. Greater Dayton is generally referred to by locals as the Miami.

As of the census of 2000, there were 166,179 people, 67,409 households, and 37,614 families residing in the city. The population density was 1,150.3/km² (2,979.3/mi²). There were 77,321 housing units at an average density of 535.2/km² (1,386.3/mi²). The racial makeup of the city was 53.40% White, 43.10%% Black or African American, 0.30% Native American, 0.65% Asian, 0.04% Pacific Islander, 0.70% from other races, and 1.83% from two or more races. 1.58% of the population were Hispanic or Latino of any race. Dayton remains largely segregated, with African Americans residing on the West and Whites on the East in the City Proper.