High Quality Content by WIKIPEDIA articles! Elizabeth is a city in Union County, New Jersey, United States. As of the 2010 United States Census, the city had a total population of 124,969, retaining its ranking as New Jersey`s fourth largest city (by population) with an increase of 4,401 residents (an added 3.7%) from its 2000 Census population of 120,568. It is the county seat of Union County.