Union County is a county located in the U.S. state of New Jersey. As of the 2010 United States Census, the population was 536,499, an increase of 13,958 (2.7%) from the 522,541 enumerated in the 2000 Census, making it the seventh-most populous county in the state. It is part of the New York Metropolitan Area. Its county seat is Elizabeth. The Bureau of Economic Analysis ranked the county as having the 119th-highest per capita income of all 3,113 counties in the United States (and the eighth-highest in New Jersey) as of 2009. A study by Forbes.com determined Union County pays the second-highest property taxes of all counties in the nation. With more than 5,000 persons per square mile on average, Union County is one of the most densely populated counties in America.
Union County was formed on March 19, 1857, from portions of Essex County.