Essex County is a county in the northeastern part of the U.S. state of New Jersey. As of the 2018 Census estimate, the county's population was 799,767, making it the state's third-most populous county, an increase of 3.1% from the 2010 United States Census, when its population was enumerated at 783,969, in turn a decrease of 1.2% (9,664 fewer residents) from the 793,633 enumerated in the 2000 census. In 2010, the county dropped down to third-largest, behind Middlesex County, and was one of only two counties in the state to see a decline between 2000 and 2010. Its county seat is Newark, the most populous city in the state.