Union County is located in the U.S. state of New Jersey. It is part of the New Jersey Metropolitan Area. Its county seat is Elizabeth. Union County ranks 92nd among the highest-income counties in the United States with its per capita income being $26,992.Union County has a total area of approximately 106 square miles of which 98% is land and 2% water. As of the 2000 census, there were 522,541 people, 186,124 households, and 133,264 families residing in Union County, NJ.