- Western Terminus:
- Montauk Highway (CR 80) and Knoll Road in Shinnecock Hills
- Eastern Terminus:
- Hill Street and Tuckahoe Lane in Southampton
- 2.79 miles
Montauk Highway is the southernmost major east/west route in Suffolk County. Until 1972, NY 27A extended along Montauk Highway from Amityville all the way to Southampton, where it became NY 27, which follows Montauk Highway to its eastern terminus at Montauk Highway. In 1972, almost all of the portion of NY 27A between Oakdale and Southampton was decommissioned. Most of this section became CR 85 and CR 80. A short section of Montauk Highway still remains under state jurisdiction from the eastern terminus of CR 80 in Shinnecock to Southampton. It has NY 27A reference markers and a reference route number of 900W, although there are no route shields so as not to confuse drivers. At the eastern terminus of this section, Montauk Highway changes names to become Hill Street. Before 1972, NY 27A followed Hill Street and Hampton Road through Southampton to the point where Hampton Road meets NY 27 and changes names to become Montauk Highway once again. Today, Hill Street and Hampton Road are locally maintained by the Village of Southampton.