Middletown is a city located in Butler and Warren counties in the southwestern part of the U.S. state of Ohio. The population as of the 2020 census was 50,987. It is part of the Cincinnati metropolitan area, located 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.