郡道
County Route 21 is a two lane, highway running from Brookhaven to Rocky Point. Its southern terminus is at CR 80 south of the interchange between CR 16 and NY 27 (which includes Yaphank Avenue in the interchange) in Brookhaven. The highway heads northward and terminates at an intersection with NY 25A in Rocky Point. CR 21 was added to the Suffolk County highway system on January 27, 1930.