It runs for 13.60 miles (21.89 km)[1] from Sound Avenue in Mattituck to New York State Route 25 (NY 25) just outside the village of Greenport.

Between Hashamomuck Pond and Greenport West, a section of Middle Road near a motel with the Long Island Sound in the back yard is still paved with concrete, as it was commonly done during the late 1920s and early 1930s.

[3] Along the border of Greenport, the road encounters a former KOA Campground, which today is the privately owned Eastern Long Island Kampground.

[5] CR 27 was originally a two-lane road[6] before the Suffolk County Department of Public Works (SCDPW) widened the west half of the route to four lanes in the early 1970s.

[7][8] A four-lane southerly bypass of Wickham Avenue was built as part of the project and designated CR 27B.

[9] Part of the reason SCDPW widened Middle Road was in anticipation of the formerly proposed North Fork extension of the Long Island Expressway (LIE).