Western Australia Day (formerly known as Foundation Day)^[1][2] is a public holiday in Western Australia, celebrated on the first Monday in June (officially on 1 June) to commemorate the founding of the Swan River Colony in 1829. Because of the celebration of Western Australia Day, WA is the only Australian state or territory that does not celebrate the Queen's Birthday Holiday in June; it is held in September or October instead.

HMS Challenger, under Captain Charles Fremantle, anchored off Garden Island on 25 April 1829. Fremantle officially claimed the western part of Australia for Britain on 2 May. The merchant vessel Parmelia, with Stirling, other officials and civilian settlers on board, sighted the coast on 1 June. It anchored in Cockburn Sound on 2 June. Another warship, HMS Sulphur, arrived on 6 June, carrying the British Army garrison. The Swan River Colony was officially proclaimed by Stirling on 11 June.