Essex County is a county in the northeastern part of the U.S. state of New Jersey. As of the 2016 Census estimate, the county's population was 796,914, making it the state's third-most populous county, an increase of 1.7% 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.