Union City is a city in the northern part of Hudson County, in the U.S. state of New Jersey. As of the 2020 United States census, the city was the state's 18th-most-populous municipality, with a population of 68,589, an increase of 2,134 from the 2010 census count of 66,455, which in turn had reflected a decline of 633 from the 67,088 counted in the 2000 census. As of the 2010 Census, among cities with a population of more than 50,000, it was the most densely populated city in the United States, with a density of 54,138 per square mile of land. The Census Bureau's Population Estimates Program calculated that the city's population was 65,366 in 2022, ranking the city the 590th-most-populous in the country.