Its eastern terminus is at a junction with NY 37 just east of the village limits in the town of Massena.

The route was extended east into Massena in the 1950s after NY 37 was realigned to follow a new bypass around the village.

Most of NY 37B west of Massena ran through a low-lying area along the St. Lawrence River.

The route heads to the northeast, paralleling the Grasse River as it passes a small number of homes and businesses located in the otherwise rural town.

[3] NY 37B turns south at the interchange, becoming Parker Avenue and crossing over the Grasse River to meet East Orvis Street on the southern riverbank.

West of Massena, the highway was routed on Town Line Road and River Road to a junction east of Waddington, where Route 32 continued west on modern NY 37 to Waddington.

[2] In the mid-to-late 1950s, NY 37 was rerouted to follow a new bypass around the southern edge of Massena.

[13] As part of the seaway's construction, a low-lying area in Ontario and New York between Waddington, New York, and Cornwall, Ontario, would be inundated with water in order to create a navigable channel through the Long Sault rapids and to allow hydroelectric stations to be established immediately upriver from Massena and Cornwall.

[10] On July 1, 1958, the intentional flooding was carried out via the destruction of a cofferdam upstream, creating what is now known as Lake St. Lawrence[14] and inundating the majority of NY 37B west of Massena.