Marion Bay is a small township at the southern tip of the Yorke Peninsula in South Australia, Australia. At the 2011 census, Marion Bay had a population of 241.
It is surrounded by beaches and is the gateway to the Innes National Park. The close proximity of the beach and cliffs have popularized Marion Bay as a fishing destination, with Brown Beach in the nearby Innes National Park being particularly famous among recreational fisherman as a picturesque fishing destination.
In 2008, a desalination plant was commissioned to meet the water demands of the summer tourist season. A 60 kL/d sea water reverse osmosis plant now supplies the local caravan park, residents and businesses. The plant was commissioned in response to declining bore water quality and associated problems of corrosion. The plant was designed and constructed by Osmoflo.