Union County, New Jersey Union County is a county located in the U.S. state of New Jersey. As of the 2000 Census, the population is 522,541. It is part of the New York Metropolitan Area. Its county seat is Elizabeth. Union County ranks 92nd among the highest-income counties in the United States with a per capita income of $26,992. With more than 5,000 persons per square mile on average, Union County is one of the [most densely populated counties in America]. Its population density exceeds that of Fulton County, Georgia (which contains Atlanta), Denver County, Colorado (which contains Denver) and Dallas County, Texas (which contains Dallas) Municipalities Towns Townships Boroughs |