The 5th Suffolk County Legislative District (L.D.) is located in the north central section of Suffolk County encompassing the north west section of the Town of Brookhaven. The district includes Setauket, East Setauket, South Setauket, Stony Brook and parts of Port Jefferson Station, Terryville, Coram and Centereach. The district also includes the following villages: Belle Terre, Old Field, Port Jefferson and Poquott. The district is bounded roughly by the Long Island Sound to the north, Route 112 to the east, Middle Country Road to the south and the Town of Smithtown to the west.
 
The 5th LD consists of fifty-six (56) election districts (E.D.’s) with 46,713 registered voters.