Xenia is a city in and the county seat of Greene County, Ohio, United States. The municipality is located in southwestern Ohio 21 miles from Dayton and is part of the Dayton Metropolitan Statistical Area, as well as the Miami Valley region. The name comes from the Greek word Xenia, which means "hospitality".As of the 2010 census, the city had a population of 25,719. Xenia is the third largest city by population in Greene County, behind Fairborn and Beavercreek. It serves as the county seat of Greene County, being at the geographical center, and housing the County Courthouse, the County Sheriff's Department, Jail, and other Government departments. By population, it is the largest place in the United States whose name begins with the letter X.