Lebanon is a city in and the county seat of Warren County, Ohio, United States. The population was 20,841 at the 2020 census. It is part of th…Lebanon is a city in and the county seat of Warren County, Ohio, United States. The population was 20,841 at the 2020 census. It is part of the Cincinnati metropolitan area. Lebanon is in the Symmes Purchase. The first European settler in what is now Lebanon was Ichabod Corwin, uncle of Ohio Governor Thomas Corwin, who came to Ohio from Bourbon County, Kentucky, and settled on the north branch of Turtle Creek in March 1796. The site of his cabin is now on the grounds of Berry Intermediate School on North Broadway and is marked with a monument erected by the Warren County Historical Society.