Establishment In the 1930 renumbering of state highways in New York, NY 72 became part of NY 21, a new route extending from the Pennsylvania state line at Troupsburg to Pultneyville. It followed what is now NY 36 from the state line to Hornell and modern County Route 121 (CR 121), NY 415, and NY 371 between Loon Lake and North Cohocton (via Cohocton). The remainder of NY 21 roughly followed its current alignment. At the same time, what is now NY 21 from Andover to Hornell was designated as the western half of NY 17F while the section between Loon Lake and modern NY 415 was assigned NY 371. The remaining piece around Wayland was part of NY 2 south of Wayland and part of the new NY 39 from Wayland to Cohocton. NY 39 overlapped NY 21 from Cohocton to Naples, where it forked from NY 21 and continued east on modern NY 245. Several portions of current NY 21 south of Naples had carried designations prior to 1930. In 1924, the Andover–Hornell segment was designated as part of NY 17; at the same time, the short piece between modern NY 415 and the center of Wayland became part of NY 4. By 1926, the portion connecting Wayland to Naples was included in the new NY 52. NY 4 was renumbered to NY 2 in 1927 to eliminate numerical duplication with the new US 4. Realignments and truncations The alignments of NY 21 and NY 371 between Loon Lake and Cohocton were flipped , routing NY 21 through the village of Wayland instead. The realignment extended NY 21's overlap with NY 39 west to Wayland and created an overlap with NY 2 south of the village. NY 2 was absorbed into an extended US 15 (now NY 15) by the following year. In the early 1940s, the NY 17F designation was eliminated and replaced with an extended NY 36 from Andover to Hornell. The alignments of NY 36 and NY 21 south of Hornell were flipped in the early 1950s, placing both routes on their current alignments south of the city. On April 1, 1980, NY 21 was truncated to its present northern terminus at NY 104 in Williamson as part of a highway maintenance swap between New York State and Wayne County. In the swap, ownership and maintenance of NY 21 north of Williamson was transferred from