The Thousand Islands Parkway begins at a split with Highway 401 on the outskirts of Gananoque. There is no access from westbound Highway 401 to the parkway nor from westbound on the parkway to eastbound Highway 401. However, immediately east of the split, both highways interchange with the sole remaining portion of Highway 2 under provincial jurisdiction. East of this point the three diverge into the rugged terrain of the Frontenac Arch, a protrusion of the Canadian Shield southward into New York state. In this area, the soil is underlain by layers of Paleozoiclimestone and a granite bedrock. The granite often extends above the ground surface as large rock outcroppings. Both layers are prominent in the Jones Creek ravine. At its midpoint, the parkway interchanges with Highway 137, an extension of Interstate 81 which serves as the Ontario approach to the internationalThousand Islands Bridge. It continues northeast, serving the riverside communities of Darlingside, Rockport, Narrows, La Rue Mills and Mallorytown Landing. At Butternut Bay, the Thousand Islands Parkway merges into Highway 401 eastbound and a left-hand exit provides access to the parkway from westbound Highway 401. Throughout most of the length of the parkway, a recreational trail parallels to the north. The Thousands Islands Parkway follows what was the original alignment for Highway 401. However, because of the residential properties and the scenic nature of the route, a new inland route was constructed through the mid-1960s. The recreational trail follows the right-of-way for the westbound lanes, which were never completed.
History
While today only a two-lane road, it was a divided and paved four lane roadway in the early 1940s. The St. Lawrence River Road was given the designation of Highway 2S in 1947. This designation remained in place for several years, until the entire route was renumbered as Highway 401 by the end of 1952. Initially, the parkway was intended as the route of Highway 401 between Gananoque and Brockville. However, when the Department of Highways encountered severe local resistance, it was instead decided that a new bypass should be built further inland. This bypass opened on October 11, 1968, at which point the entire parkway once again became Highway 2S. This designation would also only last for just under two years. On September 8, 1970, the DHO transferred the jurisdiction over the parkway to the St. Lawrence Parks Commission; it was subsequently renamed as the Thousand Islands Parkway.