Essex County is located in the northeastern part of the U.S. state of New Jersey, and is one of the centrally located counties in the New York metropolitan area. As of the 2020 census, the county was the state's second-most populous county, with a population of 863,728, its highest decennial count since the 1970 census and an increase of 79,759 (+10.2%) from the 2010 census count of 783,969. The county is part of the North Jersey region of the state.

North Jersey comprises the northern portions of the U.S. state of New Jersey between the upper Delaware River and the Atlantic Ocean. As a distinct toponym, North Jersey is a colloquial one rather than an administrative one, reflecting geographical and perceived cultural and other differences between it and the southern part of the state.