The highway enters Au Sable Forks from the south on South Main Street and becomes North Main Street upon crossing the west branch of the river and entering Clinton County and the town of Black Brook. NY 9N immediately turns east upon crossing the river, following Ausable Street out of the hamlet and along the northern edge of the Ausable River into the town of Au Sable. Here, NY 9N meets I-87 one final time at exit 34 just southwest of the village of Keeseville. NY 9N continues on into Keeseville, where it meets NY 22 once again at an intersection across the river from the village center. NY 22 and NY 9N come together once more, overlapping for to an intersection with US 9 a short distance downstream from the center of Keeseville. NY 9N comes to an end here while NY 22 turns south onto US 9.