Middletown Township is a township in northern Monmouth County, in the U.S. state of New Jersey. As of the 2020 United States census, the township was the state's 20th-most-populous municipality and the largest in the county, with a population of 67,106, an increase of 584 (+0.9%) from the 2010 census count of 66,522, which in turn reflected an increase of 195 residents (0.3%) from its population of 66,327 at the 2000 census, when it was the state's 17th-most-populous municipality.