Elizabeth is a city and the county seat of Union County, in the U.S. state of New Jersey. As of the 2020 U.S. census, the city had a total population of 137,298, making it New Jersey's fourth-most-populou…Elizabeth is a city and the county seat of Union County, in the U.S. state of New Jersey. As of the 2020 U.S. census, the city had a total population of 137,298, making it New Jersey's fourth-most-populous city, after neighboring Newark, Jersey City, and Paterson. The 2020 population was an increase of 12,329 from the 124,969 counted in the 2010 census. The Census Bureau's Population Estimates Program calculated that the city's population was 135,407 in 2021, ranking the city the 207th-most-populous in the country.