Dark Island, a prominent feature of the Saint Lawrence Seaway, is located in the lower (eastern) Thousand Islands region, near Chippewa Bay. It is a part of the Town of Hammond, in St. Lawrence County, New York.

The Thousand Islands constitute a North American archipelago of 1,864 islands that straddles the Canada–US border in the Saint Lawrence River as it emerges from the northeast corner of Lake Ontario. They stretch for about 50 miles (80 km) downstream from Kingston, Ontario. The Canadian islands are in the province of Ontario and the U.S. islands in the state of New York.