Milltown is a borough in Middlesex County, in the U.S. state of New Jersey. The borough is nestled within the heart of the Raritan Valley region, with Lawrence Brook flowing through the center of the community. As of the 2020 United States census, the borough's population was 7,037, an increase of 144 from the 2010 census count of 6,893, which in turn reflected a decrease of 107 from the 7,000 counted in the 2000 census.