Union City is a city in the northern part of Hudson County, New Jersey, United States. According to the 2010 United States Census the city had a total population of 66,455, reflecting a decline of 633 (−0.9%) from the 67,088 counted in the 2000 Census, which had in turn increased by 9,076 (+15.6%) from the 58,012 counted in the 1990 Census. The Census Bureau's Population Estimates Program calculated that the city's population was 67,982 in 2019, ranking the city the 540th-most-populous in the country. 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.Union City was incorporated as a city by an act of the New Jersey Legislature on June 1, 1925, with the merger of Union Hill and West Hoboken Township. The city's name marks the combination of the two municipalities.Two major waves of immigration, first of German speakers and then of Spanish speakers, greatly influenced the development and character of Union City. Its two nicknames, "Embroidery Capital of the United States" and "Havana on the Hudson", reflect important aspects of that history. Thousands visit Union City each year to see the nation's longest-running passion play and the annual Cuban Day Parade of New Jersey.
The city is notable for being the location where Mallomars were first sold and the site of the first lunch wagon built by Jerry and Daniel O'Mahoney and John Hanf, which helped spark New Jersey's golden age of diner manufacturing, for which the state is colloquially referred to by author Richard J.S. Gutman as the "diner capital of the world".