New York State Route 421 (NY 421) is a short state highway located within Adirondack Park in the southeastern corner of St. Lawrence County, New York, in the United States. It is a narrow, two-lane spur route connecting NY 30 to Horseshoe Lake by way of Tupper Lake. A dead end sign is posted immediately off NY 30, the only route with which it intersects. The entire road is located in the town of Piercefield, although that name is not posted on NY 421. The route offers access to several picnic and snowmobile areas.

New York State Route 30 (NY 30) is a state highway in the central part of New York in the United States. It extends for 300.71 miles (483.95 km) from an interchange with NY 17 in the Southern Tier to the US–Canada border in the state's North Country, where it continues into Quebec as Route 138. On a regional level, the route serves to connect the Catskill Park to the Adirondack Park. In the latter, NY 30 is known as the Adirondack Trail. Aside from the state parks, the route serves the city of Amsterdam and several villages.