Middle Island is a hamlet and census-designated place (CDP) in Suffolk County, New York, United States. The population was 10,483 at the 2010 census. It is situated between the hamlets of Coram and Ridge, to the west and east, respectively, and Rocky Point and Yaphank to the north and south. The name derives from the fact that it lies approximately halfway between the eastern and western ends of Long Island (Montauk Point and the East River) as well as halfway between the northern and southern boundaries (the Long Island Sound and the Atlantic Ocean).
Middle Island is a community in the Town of Brookhaven served by the Longwood Central School District, which at 58 square miles (150 km2) is the largest school district on Long Island. The Longwood Public Library is located in Middle Island.
Parks within Middle Island include Cathedral Pines County Park (formerly a Boy Scout camp) and the adjacent Prosser Pines County Park. Middle Island is surrounded by three public golf courses. Middle Island Country Club and Spring Lake Golf Club are both within Middle Island; Mill Pond Golf Course is just to the south, in Yaphank.
Middle Island is located at 40°53′6″N 72°56′36″W (40.885095, −72.943452).
According to the United States Census Bureau, the CDP has a total area of 8.3 square miles (21.5 km2), of which 8.2 square miles (21.3 km2) is land and 0.077 square miles (0.2 km2), or 0.71%, is water.
Middle Island has many lakes such as Spring Lake, Artist Lake, and Pine Lake (which has a new dock).