NY 12B begins at an intersection with NY 12 (North Main Street / Utica Road) in the village of Sherburne. From NY 12, NY 12B proceeds north on North Main Street, while NY 12 proceeds northeast on Utica Road. A mix of residences and businesses parallel NY 12B, which leaves the village for the town of Sherburne to the northwest. NY 12B parallels a railroad line to the north, passing Baldwin Station, where the railroad crosses. The route becomes rural, bending to the north through Sherburne and paralleling the Springfield River. The two-lane rural roadway continues north, crosses the county line into Madison County and entering the village of Earlville. In Earlville, NY 12B doubles as North Main Street, a two-lane residential street that crosses through.
