Afon Irfon is a river in Powys, Wales. It flows from the upper slopes of Bryn Garw in the Cambrian Mountains, through the Abergwesyn Valley, past the Nant Irfon National Nature Reserve in the hills above the village of Abergwesyn, and through Llanwrtyd Wells to its confluence with the River Wye at Builth Wells. The source of the Irfon is in the so-called 'Desert of Wales'.

Abergwesyn is a village in the Welsh county of Powys, in mid-Wales, at the start of the Abergwesyn valley and at the confluence of the Afon Irfon and the Afon Gwesyn. It is 52 miles (84 km) from Cardiff and 158 miles (254 km) from London.