Newark is the most populous city in the U.S. state of New Jersey, the county seat of Essex County, and a principal city of the New York me…Newark is the most populous city in the U.S. state of New Jersey, the county seat of Essex County, and a principal city of the New York metropolitan area. As of the 2020 census, the city's population was 311,549. The Population Estimates Program calculated a population of 304,960 for 2023, making it the 66th-most populous municipality in the nation.