Brentwood is a hamlet in the Town of Islip in Suffolk County, New York, United States, and has a total area of 11.0 square miles (28 km2). Brentwood is the site of Pilgrim State Hospital (once one of the world’s largest hospitals and psychiatric institutions), now known as Pilgrim Psychiatric Center. A 52-acre (0.21 km2) portion of the psychiatric center was converted into the Brentwood State Park athletic field complex
Long Island Expressway forms a natural boundary to the north. The interchange of Long Island Expressway and Sagtikos Parkway occupies the northwest portion of the hamlet, on the corner of the Suffolk County Community College Grant Campus on Crooked Hill Road. Southern State Parkway partially passes through the southeast boundary and interchanges with Islip Avenue, partially forming the southeast boundary up until Suffolk Avenue to the north of the interchange.
Suffolk Avenue serves as main to and from west-east, while Washington Avenue does north-south. Along the main road of Suffolk Avenue is the Brentwood Train station by the LIRR. Notable landmarks include Brentwood State Park, Ross Memorial Park, Timberline Park, Ellery park, Gil Hodges Park, Modern Times Park and Heartland Golf Park.
Other educational buildings within the hamlet are Brentwood Freshman Center, Pine Park Elementary School, North Elementary School, Gail E. Kirkham Northeast Elementary School, East Middle School, Ross Center High School, Eastern Suffolk Boces Adult Education Center, South Middle School, Frank J. Cannon Southeast Elementary School, Sonderling Center High School, Laurel Park Elementary School and Brentwood Union Union Free School District.
Brentwood is protected by the Brentwood Fire Department, a volunteer fire department. The area of responsibility spans 24 square miles (62 km2) and covers the areas of Brentwood, North Bay Shore, and Baywood.
Brentwood is served by the Brentwood station on the Ronkonkoma Branch of the Long Island Rail Road. The station also serves as a hub for Suffolk Transit buses.
Brentwood Coordinates: 40°46′54″N 73°14′39″W