High Quality Content by WIKIPEDIA articles! New York State Route 21 (NY 21) is a state highway extending for 99.99 miles (160.92 km) through the western part of New York in the United States. The southern terminus of the route is at NY 417 in Andover. The northern terminus is at NY 104 in Williamson. In between, NY 21 serves the cities of Hornell and Canandaigua and intersects several major east–west routes, including the Southern Tier Expressway near Hornell, the conjoined routes of U.S. Route 20 (US 20) and NY 5 in Canandaigua, the New York State Thruway in Manchester, and NY 31 in Palmyra.