NY 73 was assigned as part of the 1930 renumbering of state highways in New York; however, it did not initially follow any of its modern routing. It began at an intersection with NY 28N in Tahawus and followed the Blue Ridge Road east to US 9 in North Hudson. From there, it overlapped US 9 south to Schroon, where it proceeded eastward on the former legislative Route 48 to Ticonderoga, where it ended at a junction with NY 22. At the time, modern NY 73 from Lake Placid to Keene—identical to the old North West Bay Road east of the Lake Placid area—was assigned NY 86A. The remainder of what is now NY 73 from Keene south to Underwood was designated as NY 427 within a year's time.