The highway begins at an intersection with NY 86 in the village of Lake Placid and ends at a junction with U.S. Route 9 (US 9) north of the hamlet of Underwood in the extreme southwestern corner of the town of Elizabethtown.

In the early 19th century, Lake Placid and Keene were connected by the North West Bay Road, an east–west highway linking Hopkinton to Westport.

There, County Route 35 (CR 35) merges from the northwest, providing a bypass around the village of Lake Placid to NY 86.

The highway crosses the West Branch of the Ausable River, intersecting with CR 21 at an elevation of 1,800 feet (550 m).

[3][4] Cascade Road makes several turns, passing south of the Craig Wood Golf Course.

NY 73 continues, eventually crossing the Ausable River branch, later coming in the towns of Elizabethtown and North Hudson.

The overlap with NY 9N accumulated an average of 4,360 vehicles, with the stretch up to the control station at having a less amount of traffic.

Many of the early settlers arrived in the region by traveling along a rough and nearly unusable highway connecting what became Keene to Jay in the north and Lewis in the east.

[5] By 1810, part of the crude roadway had been supplanted by a privately funded highway leading westward from Westport to at least North Elba and possibly to Saranac Lake by way of Keene.

[6] Initially, the state highway was poorly constructed and largely impassable, mirroring the condition of the roadways that preceded it.

An act passed by the state legislature on June 19, 1812, indicated that the funds that had been allocated to the highway were "entirely inadequate to open and improve" the road.

On April 17, 1816, the state attempted to correct the issue by approving a measure that appointed two sets of commissioners to oversee the reconstruction of the highway.

[15] 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.

[28] On September 14, 1994, the state of New York signed a proposal to turn NY 73 into a scenic byway into law.

[41] Note: Although NY 73 is signed east-west, traffic data reports, inventory listings and reference markers indicate that it is a north-south route.