Castle Hill is an electoral district of the Legislative Assembly in the Australian state of New South Wales. It is represented by Mark Hodges of the Liberal Party.

It is an conservative urban electorate in the Hills District in Sydney's north west.

The electorate formed during the redistribution in 2004 and replaced the former electorate of The Hills, which was abolished at the same time. It was first contested at the 2007 election, when it was won by Michael Richardson, previously the member for The Hills.

While the Hills District has long been Liberal heartland, Castle Hill is considered a particularly safe seat even by Hills standards. Counting its time as The Hills, the Liberals have always won an outright majority in this seat on the first count. However, in recent years, Labor has run dead here;^{[citation needed]} in the three elections since its creation, Labor has been lucky to win 30 percent of the two-party vote.

After the 2015 election, it was the safest seat in the state, with a 29.4 percent swing needed for Labor to win it.

It was retained by the Liberal Party with a 50.7% first round vote in the 2023 state election.

On its current boundaries, Castle Hill takes in the suburbs of Annangrove, Beaumont Hills, Box Hill, Glenhaven, Nelson and parts of Castle Hill, Dural, Kellyville, North Kellyville, Kenthurst, Maraylya, Middle Dural, Round Corner and Rouse Hill.^[1]