Mundoo Island is a locality in the Australian state of South Australia located on Mundoo Island and some adjoining water at the southern end of Lake Alexandrina about 87 kilometres (54 mi) south-east of the state capital of Adelaide.

[4][1] Its boundaries were created on 31 August 2000 for the "long established name", which is derived from the island and ultimately from an Aboriginal word mundo, which means "mud" or "filth".

[1] The locality consists of Mundoo Island and a portion of the following waterways adjoining the island: the channel known as the Lower Murray (or the Goolwa) in the north; Boundary Creek to the east and the south-east; the Coorong Channel in the south; the Mundoo Channel in the south-west; and Holmes Creek to the west and the north-west.

[1][9] The land within the locality is occupied by the privately owned Mundoo Island Station which has been operation since 1843.

[11][10] Mundoo Island is located within the federal division of Mayo, the state electoral district of Finniss, and the local government area of the Alexandrina Council.