O'Sullivan Beach is a seaside suburb in the southern Adelaide metropolitan area, within the City of Onkaparinga. O'Sullivan Beach has a unique postcode of 5166. The very first development to occur along the coast of O'Sullivan Beach can be traced back to pre-colonization times, almost 40,000 years ago. The Aboriginal Kaurna people used the co…O'Sullivan Beach is a seaside suburb in the southern Adelaide metropolitan area, within the City of Onkaparinga. O'Sullivan Beach has a unique postcode of 5166. The very first development to occur along the coast of O'Sullivan Beach can be traced back to pre-colonization times, almost 40,000 years ago. The Aboriginal Kaurna people used the coastal area of O'Sullivan Beach as a place for seasonal residence. In particular the mouth of Christie Creek was used as a Kaurna campsite. Christie Creek was also one of the last recorded sites where traditional burial practices were observed.