The area was originally called Cabramatta an aboriginal word for place of the cobra grub. It was later named Rossmore, a Scottish name refering to high ground by John Dickson a Scottish engineer who was granted 3,000 acres of land here by Governor Macquarie. A number of other settlers received land grants in the area including Barker, Riley, Moore and Bell.
The area was initially used for wheat and sheep farming and later for dairying, poultry farming and orchards. The bushranger Jack Donahoe was shot by an ex soldier, Mugglestone on Robert Lowe’s property just south of Bringelly Rd in 1830.
After World War 1 Ashley McCann bought 1,400 acres at Rossmore for dairy farming and named the property Allenby after General Allenby the hero of the 4th Light Horse.
Until 1948 Rossmore was part of Nepean Shire. This local government area no longer exists and was divided between Camden Liverpool and Penrith Councils. The southern third of the suburb of Rossmore is now in Camden Local Government Area.
From 1950s the area was settled by immigrants from Europe who established small farms and market gardens providing food for Sydney markets. The area continues to perform this function although large scale development is planned as part of the South West Sydney Growth Area.