Castlereagh was an electoral district of the Legislative Assembly in the Australian state of New South Wales originally created in 1904, partly replacing Coonamble and named after the Castlereagh River. In 1920, with the introduction of proportional representation, it was absorbed into Wammerawa, along with Mudgee and Liverpool Plains. It was recreated in 1927 and abolished in 1991.
References
Electoral district of Castlereagh Wikipedia(Text) CC BY-SA