New York State Route 420

New York State Route 420
Map of northeastern St. Lawrence County with NY 420 highlighted in red
Route information
Maintained by NYSDOT
Length:	11.92 mi (19.18 km)
Existed:	1930 – present
Major junctions
South end:	US 11 in
North end:	NY 37 in Massena
Location
Counties:	St. Lawrence
Highway system
New York Highways Interstate U.S. State Reference Parkways ← NY 419 NY 421 →

New York State Route 420 (NY 420) is a north–south state highway in St. Lawrence County, New York, in the United States. The southern terminus of the route is at an intersection with U.S. Route 11 (US 11) in the town of . Its northern terminus is at a junction with NY 37 in the village of Massena. NY 420 passes through undeveloped regions of St. Lawrence County for most of its routing and briefly overlaps with NY 11C in the hamlet of Winthrop.

NY 420 was originally part of Route 32, an unsigned legislative route created by the New York State Legislature in 1908. The Winthrop–Massena portion of Route 32 became part of the signed NY 56 in the mid-1920s; however, NY 56 was realigned in 1927 to follow a new alignment well to the south of Winthrop. The former routing of NY 56 between Winthrop and Massena was redesignated as NY 420 as part of the 1930 renumbering of state highways in New York. NY 420 was extended southward to its current terminus south of Winthrop in 1980.

NY 420 begins at an intersection with US 11 in the town of . The route heads north as a two-lane highway through forested areas and across both branches of the St. Regis River to the hamlet of Winthrop, the first area of significant development along the highway. Here, the two branches of the St. Regis River converge and NY 420 meets NY 11C. NY 420 turns northeastward, overlapping NY 11C for two blocks before splitting from it in the center of Winthrop.