Most of the route passes through rural areas, and the portion southeast of Carthage parallels either the Black River or a tributary of it.

The route heads east, passing through a predominantly residential area of the town of Watertown.

Roughly 1 mile (1.6 km) east of NY 12, the homes give way to open fields as the route enters the town of Rutland.

NY 126 passes east–west through the center of the small, mostly residential community before turning to the northeast as it leaves the hamlet.

[3] The route continues onward through open fields to the village of West Carthage, where it becomes known as Champion Street and meets NY 26 west of the village center at Martin and North Broad Streets.

[3] Now in the town of Croghan, NY 126 becomes a rural connector highway once again as it runs in close proximity to the Black River.

The two separate about 2 miles (3.2 km) south of the county line as NY 126 leaves the riverbank and follows a more northeasterly routing than the river through the town.

[3] East of Naumburg, NY 126 follows the north bank of the Beaver River as it proceeds through rural Croghan.

[5] The portion of NY 26 between Carthage and Antwerp was rerouted in 1960 to follow a new alignment via Calcium, part of which used a new state highway northeast of Watertown.