In Sydney’s outer northwest, Castle Hill is north of Baulkham Hills and is surrounded by the suburbs of Bella Vista, Kellyville, Glenhaven, Cherrybrook, West Pennant Hills and North Rocks. Castle Hill has its own golf course and hospital, the Hills Private Hospital. The Bidjigal Reserve, which is in the southern part of the suburb, commemorates the original occupiers of the land, the Bidjigal people.
Castle Hill is just north of the M2 Motorway (tolled) to the city. Windsor Road runs north from Castle Hill through Rouse to Windsor in the Hawkesbury Valley.