Castlereagh Highway is a state highway located in New South Wales and Queensland, Australia. From north to south the highway traverses South West Queensland and the North West Slopes, Orana, and Central West regions of New South Wales. The highway is part of the Great Inland Way linking Sydney and Cairns, and provides all-weather access to rugged black opal country of Lightning Ridge. Castlereagh Highway was named after the Castlereagh River, which it parallels for most of its journey north from Gilgandra. Route Castlereagh Highway commences at an intersection with Carnarvon Highway, south of , Queensland, and heads in a south-westerly direction via Dirranbandi to Hebel, where it crosses the state border with New South Wales just beyond and continues in a southerly direction, past Lightning Ridge to Walgett, where it crosses the Barwon and Namoi Rivers and meets the Gwydir and Kamilaroi Highways. Continuing south through Coonamble, the highway crosses the Castlereagh River and meets the Oxley and Newell Highways in Gilgandra. It continues in a south-easterly direction through Dunedoo, sharing a short concurrency with Golden Highway, continues through the regional centres of Gulgong and Mudgee, through Ilford and the junctions of Bathurst-Ilford Road and Bylong Valley Way, before eventually terminating at an interchange with Great Western Highway at Marrangaroo, north-west of Lithgow. History The passing of the Main Roads Act of 1924 through the Parliament of New South Wales provided for the declaration of Main Roads, roads partially funded by the State government through the Main Roads Board (later the Department of Main Roads, and eventually Transport for NSW). Main Road No. 55 was declared from the intersection with Great Western Highway near Marrangaroo, via Ilford, Mudgee, and Gulgong to Craboon (and continuing northwards via Coolah eventually to the intersection with Oxley Highway at Mullaley), Main Road No. 56 was declared from Walgett, via Coonamble to Gilgandra (and continuing southwards via Dubbo, Forbes, Cowra, Yass and Canberra eventually to the intersection with Queanbeyan-Braidwood Road, today Kings Highway, at Queanbeyan), and Main Road No. 205 was declared from Craboon via Dunedoo to Mendooran (and continuing northwards via Tooraweenah to Coonamble), on the same day, 8 August 1928. With the passing of the Main Roads (Amendment) Act of 1929 to provide for additional declarations of State Highways and Trunk Roads, these were amended to Trunk Roads 55 and 56 and Main Road 205 on 8 April 1929. Trunk Road 77