Castlereagh River
The Castlereagh rises 20 km west of Coonabarabran in the heart of the Warrumbungle mountains at an elevation of about 850 metres. From its commencement upstream in the mountains the river initially flows east through the town of Coonabarabran. It then arcs round south and southwesterly to the village of Ulamambri, then south to Binnaway, and SSW to the small town of Mendooran which lies at the eastern side of the river's hook-shape. From here the Castlereagh flows in a westerly direction at the flattened bottom of the hook and then turns north-westerly towards the town of Gilgandra. From Gilgandra it continues to run northwesterly across the plains through Gulargambone and Coonamble, then continuing across expansive plains, with no urban centres, where elevations are less than 200m, until it joins the Macquarie River at its uppermost reaches beyond the Macquarie Marshes. Its confluence with the Macquarie is about 65 km SW of Walgett. Not far from the Castlereagh/Macquarie confluence the Macquarie itself joins the Barwon River at a place about halfway between Walgett and Brewarrina.
Castlereagh (County Down townland)
Under the Irish Poor Laws, Castlereagh townland gave its name to the surrounding Castlereagh electoral division within the Belfast poor law union. After the Local Government (Ireland) Act 1898, the County Down portion of the union became the Belfast No. 2 rural district, later renamed Castlereagh rural district; the poor law electoral division became a district electoral division (DED). The Local Government (Boundaries) Act (Northern Ireland) 1971 specified Castlereagh DED as the nucleus of one of the 26 new local government districts, which thus was named Castlereagh district; it became Castlereagh borough in 1977 upon acquiring borough status.