Heirisson Island is an artificially created island in the Swan River in Western Australia at the eastern end of Perth Water, within the suburb of East Perth. It occupies an area of 285,600 square metres (70.6 acres), and is connected to the two foreshores by the Causeway and Boorloo Bridge. The next upstream island is Kuljak Island, then Ron Courtney Island, with no islands in the Swan River downstream between Heirisson Island and the Indian Ocean other than the artificial islet in Elizabeth Quay.

Before development, there were several small islands, surrounded by mudflats. Over the years, dredging and reclamation has created a single island, which is now a landscaped nature reserve, with a 2-kilometre (1.2 mi) walking path. The Noongar name for the area is Matagarup (meaning 'leg deep'), which has been retained for the single island after reclamation.

Heirisson Island is listed on the Western Australia Department of Aboriginal Affairs' Register of Aboriginal Sites, as ID 3589.

Heirisson Island originally consisted of six separate smaller islands surrounded by mudflats. By the 1940s, land reclamation and dredging of the Swan River to create two navigable channels saw the islands coalesce into one large island.

The area around Heirisson Island is traditionally associated with the Beeloo people, a subgroup of the Whadjuk Noongar, who knew the small islands and mudflats as Matagarup, referring to the river as being "one leg deep". The island located on either side of the current causeway bridge was known as Kakaroomup. The Matagarup mudflats were the first major crossing point upriver from the river's mouth (at Fremantle) and were an important seasonal access way over which the Beeloo gave other groups right of passage across the river.

The first European to visit the Heirisson Island area was the Dutch explorer Willem de Vlamingh in January 1697. He was exploring the Swan River in longboats but only got as far as the Heirisson Island(s) because the mudflats impeded any further progress. Heirisson Island was subsequently named after French midshipman François-Antoine Boniface Heirisson, ^[fr] who was on the French ship Naturaliste on a scientific expedition led by Nicolas Baudin between 1801 and 1804. The expedition made several journeys up the river from Fremantle in longboats and made the first maps of the Swan River. The islands were named in June 1801. James Stirling later investigated the area in 1827 just before the Swan River Colony was settled in 1829.^{[page needed]}

Before becoming a reserve the islands had been host to a shanty town and animals were seen grazing on the islands as late as the 1920s. In the late-1940s plans were drawn for the development of an extensive sporting complex on the now singular island, which was envisioned to feature an athletics stadium, an Olympic swimming pool, and 18 tennis courts; however the venture was dropped following a potential cost blowout. Other proposals for the island throughout the years include those for a motel, a golf course, a caravan park, and a cultural centre with museums and concert halls. In 1966, it was proposed to develop Heirisson Island into an aerodrome for VTOL aircraft. There were also plans to fill in the western channel of the Swan River and join the island to East Perth.

In September 1984 the Government of Western Australia erected a statue of Aboriginal warrior Yagan on the island. In 1997 the statue's head was twice removed by vandals.