Castle Hill is a suburb in the Hills District region of Sydney, New South Wales, Australia. It is located approximately 30 kilometers north-west of the Sydney central business district, and is part of the local government area of the Hills Shire.
The suburb is situated on the hills between Parramatta and Hornsby, and is bounded by the suburbs of Baulkham Hills, West Pennant Hills, Glenhaven, and Kellyville. Castle Hill is known for its leafy, residential streets, as well as its many parks and reserves, including the popular Castle Hill Heritage Park.