Highway 137 begins at the U.S. border crossing between Wellesley and Hill Islands, where it continues as south as I-81 towards Syracuse, New York. After leaving the toll plaza and passing the duty free stores, the route curves northeast where it travels past the Thousand Islands Tower observation deck before turning north. The highway crosses three spans of the Thousand Islands Bridge over the Saint Lawrence River, including a Warren truss bridge between Hill Island and Constance Island, a arch bridge between Constance and Georgina Islands, and a suspension bridge between Georgina Island and the Ontario mainland.