New York State Route 12D (NY 12D) is a north–south state highway located in the northern part of New York in the United States. 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. NY 46 and NY 294 are also present in the immediate area of the route's southern terminus. NY 12D was originally assigned as part of the 1930 renumbering of state highways in New York to most of what is now NY 12 between Boonville and Lowville. The alignments of both routes between the two locations were swapped , placing NY 12D on its current alignment from Boonville to Potters Corners (in the Town of West Turin) and on NY 26 between Potters Corners and Lowville. The overlap between NY 12D and NY 26 remained in place until the 1970s when NY 12D was realigned onto its current routing between Potters Corners and Lyons Falls, replacing then-New York State Route 337. Route description NY 12D begins at an intersection with NY 12 at the southeastern edge of the village of Boonville in northern Oneida County. While NY 12 bypasses the village to the east, NY 12D heads northwest into the village on Main Street. At Schuyler Street, NY 12D bears west for one block to Post Street, where it intersects the northern terminus of NY 46. The eastern terminus of NY 294 is located one block to the south at the junction of Post and Ford Streets. NY 12D, meanwhile, turns north at Post Street and follows the street out of the village and through the town of Boonville to the Lewis County town of Leyden. 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 later, where it intersects NY 26 at Potters Corners. NY 26 turns north here to follow the right-of-way of NY 12D; however, NY 12D turns northeast onto the right-of-way of NY 26 toward Lyons Falls. Near the western edge of the village, NY 12D passes over NY 12