Mills Reservation is a county park, consisting of a 157.15-acre (0.6360 km2) protected wooded area located in Cedar Grove and Montclair, New Jersey, United States. The reservation is maintained by the Essex County Park Commission. The reservation has several walking/jogging trails, including four major trails and numerous smaller trails. One of the four main trails leads to a cliff that overlooks the New York City skyline. Mills Reservation is located on the First Watchung Mountain, one of three Watchung Mountains which are long, low ridges of volcanic origin in northern New Jersey.