Middletown is a city in Butler and Warren counties in the southwest of the U.S. state of Ohio. The population at the 2020 census was 50,987. It is part of the Cincinnati metropolitan area, 29 miles northeast of Cincinnati and 20 miles southwest of Dayton. Formerly in Lemon, Turtlecreek, and Franklin townships, Middletown was incorporated by the Ohio General Assembly on February 11, 1833, and became a city in 1886.