Union City is a city in 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. As of the 2010 Census it was the most densely populated city in the United States, with a density of 51,810.1 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. 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 make a pilgrimage to Union City each year to see the nation's longest running passion play and the annual Cuban Day Parade of New Jersey.