Adelaide Adelaide () is the capital and most populous city of the Australian state of South Australia, and is the fifth-largest city in Australia, with a population of more than 1.1 million. It is a coastal city situated on the eastern shores of Gulf St. Vincent, on the Adelaide Plains, north of the Fleurieu Peninsula, between the Gulf St. Vincent and the low-lying Mount Lofty Ranges. It is roughly from the coast to the foothills but sprawls from Gawler at its northern extent to Sellicks Beach in the south.