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.
Activities in Mills Reservation include walking, jogging, hiking, and sightseeing of different plants and animal species, as in all forest parks. However, bike riding is prohibited by the county.
In 1954, the Essex County Park Commission received a gift of 118.9 acres from the Davella Mills Foundation. (1935-1955: Created for the Purpose of Benefiting Mankind, David Bloss Mills, Founder) David Bloss Mills, and his wife, Ella C. Mills. Mr. Mills had become wealthy from a spark plug invention which was used by Buick.
Later acreage was acquired in a swap with Newark. The park design was by the Olmsteads, who had designed Montclair's Anderson Park, New York City's Central Park, etc.
During World War Two, an anti-aircraft gun emplacement was made in Mills Reservation at the lookout point on the cliffs overlooking New York City. All that remains of this today is a circular cement platform. There are also some reports that that cliff-edge location was used as a fire-beacon station in George Washington's communication, as in the French and Indian war, and early as a smoke-signal point by the Indians. Lenape Trail runs through the park.