Fairfield is a township in far northwestern Essex County, in the U.S. state of New Jersey. As of the 2020 United States census, the township's population was 7,872, an increase of 406 (+5.4%) from the 2010 census count of 7,466, which in turn reflected an increase of 403 (+5.7%) from the 7,063 counted in the 2000 census. Fairfield was the least densely populated town in Essex County in 2020.

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.