Llanrhaeadr-ym-Mochnant () is a town, community and an ecclesiastical parish in the extreme north of Powys, Wales; about 9 miles west of Oswestry and 12 miles south of Llangollen, on the B4580. It lies near the foothills of the Berwyn mountains on the river Rhaeadr. At the top end of the valley is the Pistyll Rhaeadr waterfall, one of the Seven Wonders of Wales in the old rhyme. One mile north of the town is the hill Moel Hen-fache (515 m). The community includes the hamlet of Llanarmon Mynydd Mawr.