NY 73 was assigned as part of the 1930 renumbering of state highways in New York from NY 28N in Tahawus to NY 22 in Ticonderoga. The portion of the route from Tahawus to North Hudson followed the Blue Ridge Road; from North Hudson to Schroon, NY 73 overlapped US 9. At the time, modern NY 73 was designated as New York State Route 86A from Lake Placid to Keene. By the following year, the remainder of current NY 73 had become New York State Route 427. NY 73 was cut back to Schroon while NY 427 was replaced by an extended NY 86A . In 1952, NY 73 was extended northward to Lake Placid, supplanting NY 86A. The eastern terminus of NY 73 was moved to the vicinity of Underwood on July 1, 1972, and the former routing of NY 73 from Schroon to Ticonderoga became NY 74.