The southern terminus of the route is in the Oneida County village of Boonville, where it intersects NY 12.

The northern terminus is at a junction with NY 12 in the Lewis County village of Lyons Falls.

The eastern terminus of NY 294 is located one block to the south at the junction of Post and Ford streets.

[3] Within Leyden, NY 12D passes through largely rural terrain with the exception of a pair of roadside communities: the hamlet of Talcottville on the Sugar River, a tributary of the nearby Black River, and the community of Locust Grove at the intersection of NY 12D and Locust Grove Road.

The route crosses into West Turin roughly 1 mile (1.6 km) later, where it intersects NY 26 at Potters Corners.

[17] The former routing of NY 337 along McAlpine Street from Cherry Street to a grade crossing with the Mohawk, Adirondack and Northern Railroad, a distance of 0.03 miles (48 m), is now designated as NY 970J, an unsigned reference route.