Chatham Island is an island

Island

An island or isle is any piece of sub-continental land that is surrounded by water. Very small islands such as emergent land features on atolls can be called islets, cays or keys. An island in a river or lake may be called an eyot , or holm...

 that is located in the Great Southern region of Western Australia

Western Australia

Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...

. The island is approximately 1.1 kilometre (0.683510010314787 mi) offshore from D'Entrecasteaux National Park

D'Entrecasteaux National Park

D'Entrecasteaux National Park is a national park in Western Australia , south of Perth. The park is named after the French Admiral Bruni D'Entrecasteaux who was the first European to sight the area and name Point D'Entrecasteaux in 1792....

 and 3 kilometres (2 mi) offshore from Mandalay Beach.
Declared a class 1A Nature reserve in 1973 the island has a total area of 106 hectares (262 acre).

Named by George Vancouver

George Vancouver

Captain George Vancouver RN was an English officer of the British Royal Navy, best known for his 1791-95 expedition, which explored and charted North America's northwestern Pacific Coast regions, including the coasts of contemporary Alaska, British Columbia, Washington and Oregon...

aboard the HMS Discovery as Cape Chatham in 1791 the island was subsequently renamed as Chatham island.