Guttenberg is a town in the northern part of Hudson County, in the U.S. state of New Jersey. In the 2020 Census, it was the most densely populated incorporated municipality in the United States, as well as one of the most densely populated municipalities worldwide, with 57,116 inhabitants per square mile of land area. Only four blocks wide, Guttenberg has been variously ranked as the ninth-smallest municipality in the state or as the state's seventh-smallest municipality.