Castlereagh, or The Castlereagh until 1910, was an electoral district of the Legislative Assembly in the Australian state of New South Wales originally created in the 1904 re-distribution of electorates following the 1903 New South Wales referendum, which required the number of members of the Legislative Assembly to be reduced from 125 to 90.[1] It consisted of the abolished seat of Coonamble and part of the abolished seat of Dubbo and was 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,[2][3][4] replaced by Barwon in the north-west, including the towns of Narrabri and Gilgandra, and by Upper Hunter in the south-east, including the town of Mudgee.[5]