Greene County, Ohio, named for General Nathaniel Greene, the Revolutionary War Hero, was established in its present boundaries in 1819. When Ohio was admitted to the Union in 1803, Greene County stretched from Clinton County on the south to the then north line of the new state.

The oldest settlement in Greene County appears to have been Old Chillicothe (now Old Town), a village of the Shawnee Indians, which had a peak population of 1100 persons around 1779. The first white settlement in Greene County was founded by John Wilson and his sons, Amos, John, George and Daniel, who each built a log shelter at Clio (now Ferry) in the southwest corner of the county in 1796.

The first county business was transacted in a small log house located about a quarter of a mile from Alpha on the banks of the Beaver Creek. The first Court House in Xenia was finished in 1809 at a cost of $3,396. The Present Court House was built in 1902 at a approximate cost of $192,000.

Xenia, which was established as the county seat in 1804, is derived from the Greek and signifies hospitality.