The suburb is split between the Cities of Marion and Onkaparinga, and it neighbours Happy Valley, Hallett Cove, Trott Park and Darlington.

[6] Located on the foothills of the Mount Lofty Ranges and bordering the Adelaide plains, the suburb (and the hill) were named after Major Thomas O'Halloran, the first Police Commissioner of South Australia.

In an official report, O'Halloran claimed the Kaurna also used this as a weapon against the colonists by lighting fires to deliberately destroy fences, survey pegs and to scatter livestock.

Due to this regular burning, the foothills' original stringybark forests had been largely replaced with grassland by the time the first Europeans arrived.

[citation needed] West of South Road is 200 hectares (490 acres) of former farmland and commercial vineyards, Glenthorne Estate, originally a farm and horse stud owned by O'Halloran, who lived on a property nearby named Lizard Lodge.