Millville is a city in Cumberland County, in the U.S. state of New Jersey. As of the 2020 United States census, the city's population was 27,491, a decrease of 909 from the 2010 census count of 28,400, which in turn reflected an increase of 1,553 from the 26,847 counted in the 2000 census. Millville was originally incorporated as a township by an act of the New Jersey Legislature on February 24, 1801, from portions of Fairfield Township.