Sinclair Island is an island in the U.S. state of Washington. It is a part of, and lies off the western shore of mainland Skagit County. The island has a land area of 4.109 km2 (1.586 sq mi) and is home to only a few private residents.
Hood Canal is long and narrow with an average width of 1.5 miles (2.4 km) and a mean depth of 53.8 metres (177 ft).