Coordinates: 44°19′N 76°00′W / 44.317°N 76.000°W
Wellesley Island in Jefferson County, New York, United States is partially in the Town of Orleans and partially in the Town of Alexandria.
The island was named Wells Island but during his 1815 survey of the US-Canada border renamed by Captain William Fitzwilliam Owen to the current name to honor Arthur Wellesley, 1st Duke of Wellington. Several prominent points in and around the island were named after the Duke's victorious battles. None of those names stuck. The large bay around which the island folds is called Lake of the Isles, not Lake Waterloo.
The island is located 44°19′N 76°00′W / 44.317°N 76.000°W in the St. Lawrence River, which surrounds Wellesley Island on three sides. The island bounds an internal body of water, the Lake of the Isles, which nearly doubles its waterfront. The easternmost peninsula of the island lies across the Upper (American) Narrows from the Village of Alexandria Bay.