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.