The Seaway Trail enters the state's largest county along Route 12, heading northeast. It passes through Chippewa Bay and Oak Point before reaching NY 37, Route 12's northern terminus. The trail continues northeast along Route 37 to just outside the city of Ogdensburg. There, it follows NY 68, the Downtown Arterial Highway, which runs closer to the St. Lawrence River than Route 37. After crossing the Oswegatchie River mouth, the trail leaves Route 68 and winds its way through the western half of the city, eventually reaching NY 812, which it traverses for a fifth of a mile (300 m) to get back to Route 37.