Monarto South is a locality in South Australia 16 kilometres (9.9 mi) west of the Murray River. It is north of the South Eastern Freeway between the Callington and Murray Bridge exits, 65 kilometres (40 mi) south east by road from Adelaide.
In the late 1970s Monarto Junction (or "New Murray Town") was proposed to be the site of a new satellite city of Adelaide. By the turn of the century the proposal had been completely abandoned.
Monarto South took its name from the cadastral Hundred of Monarto (established 1847) centred on the original township of Monarto to the north. The name of the hundred was after "Queen Monarto", an aboriginal woman (spouse of a tribal leader) who lived in the area at the time of its proclamation.