Oregonia is an unincorporated community in northwestern Washington Township, Warren County, Ohio, United States, on the east shore of the Little Miami River about five miles northeast of Lebanon and six miles south of Waynesville.The first settlement there was around 1802, where there was a mill operated at various times by Nebo Gaunt, Ignatius Brown, and David Brown. Around 1820, it was known as Freeport. The Little Miami Railroad reached the village circa 1845.