The River Alyn (Welsh: Afon Alun) is a tributary of the River Dee, in north-east Wales. The River Alyn rises at the southern end of the Clwydian hills and the Alyn Valley forms part of the Clwydian Range and Dee Valley Area of Outstanding Natural Beauty. The main town on the river is Mold, the county town of Flintshire. It lends its name to the constituencies of Alyn and Deeside in the UK Parliament and the Senedd.