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.

Hudson County is the smallest and most densely populated county in the U.S. state of New Jersey. It lies west of the lower Hudson River, which was named for Henry Hudson, the sea captain who explored the area in 1609. Part of New Jersey's Gateway Region in the New York metropolitan area, the county seat is Jersey City, which is the county's largest city in terms of both population and area. The county is part of the North Jersey region of the state.