Piercefield is a town in St. Lawrence County, New York, United States. The population was 310 at the 2010 census.

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.