Allentown is a borough located in western Monmouth County, in the U.S. state of New Jersey, bordering adjacent Mercer County. As of the 2020 United States census, the borough's population was 1,734, a decrease of 94 from the 2010 census count of 1,828, which in turn reflected a decline of 54 from the 1,882 counted in the 2000 census. The borough is nestled within central New Jersey, and is roughly equidistant between New York City and Philadelphia.