Castlereagh Highway is a 790-kilometre (490 mi) state highway located in New South Wales and Queensland, Australia. The highway's northern terminus is at a junction with Carnarvon Highway, south of St George, Queensland. Its southern terminus is at a junction with Great Western Highway at Marrangaroo, 10 kilometres (6.2 mi) north-west of Lithgow. From north to south the highway traverses South West Queensland and the North West Slopes, Orana, and Central West regions of New South Wales.