Castle Hill is a suburb of Sydney, New South Wales, Australia, located 34 kilometres north-west of the Sydney central business district and 9.5 kilometres north of Parramatta. It is within the Hills District region, split between the local government areas of The Hills Shire and Hornsby Shire.

Greater Western Sydney (GWS) is a large region of the metropolitan area of Greater Sydney, New South Wales (NSW), Australia that generally embraces the north-west, south-west, central-west, far western and the Blue Mountains sub-regions within Sydney's metropolitan area and encompasses 11 local government areas: Blacktown, Blue Mountains, Camden, Campbelltown, Cumberland, Fairfield, Hawkesbury, Liverpool, Parramatta, Penrith and Wollondilly. It includes Western Sydney, which has a number of different definitions, although the one consistently used is the region composed of ten local government authorities, most of which are members of the Western Sydney Regional Organisation of Councils (WSROC). The NSW Government's Office of Western Sydney calls the region "Greater Western Sydney".