Warren County is a county located in the U.S. state of Ohio. As of the 2010 census, the population was 212,693. Its county seat is Lebanon. The county was erected on May 1, 1803 from Hamilton County and named for Dr. Joseph Warren, a hero of the Revolution who sent Paul Revere on his ride and who died at the Battle of Bunker Hill. Warren County is part of the Cincinnati-Middletown, OH-KY-IN Metropolitan Statistical Area.