Rooty Hill was named after a hill on Norfolk Island. The origin of this name puzzled historians for many years because the clue lay not in Blacktown City though on Norfolk Island. Governor Philip Gidley King had been in charge of the first settlement there in early 1788 and had noted that the hillside where he had built his Government House had been difficult to dig owing to the amount of tree roots beneath the surface. The hill on Norfolk became known as the rooty hill and the name is now official. When King returned to New South Wales he built the headquarters for his government reserve of 1802 at the foot of a hill that reminded him of the Norfolk Island rooty hill and there can be little doubt that he named Blacktown’s Rooty Hill after that on Norfolk where he had met his future wife and spent several happy and productive years. The name Rooty Hill first appeared on a map in 1803.
Two doubtful explanations regarding the origin of the name persist to this day. The first concerns tree roots and the trouble they presented when ploughing for cultivation – the hill was not thickly timbered and better land for cultivation was available nearby. The second explanation concerns the Hindu term ‘ruti’, meaning "food" in a colloquial sense, (it may also refer to ‘roti’, a type of wheat). Wheat was urgently needed for the expanding colony’s population and was grown in the area. A number of soldiers and marines in the colony had served in India, including Governor Lachlan Macquarie. This can be debunked quite easily because the NSW Rooty Hill was known by that name from 1802 whereas any Indian influence arrived about 1810. Furthermore, in 1803 the still-starving colony was in no position to export grain.
The purpose of Kings Rooty Hill settlement was to provide a reserve for government-owned cattle. The south-western part of this vast area (which closely follows Blacktown City’s current boundary) came to be known as the Rooty Hill Run.