Newcastle Emlyn is a town on the River Teifi, straddling the counties of Ceredigion and Carmarthenshire in West Wales. It is also a community entirely within Carmarthenshire, bordered by those of Llangeler and Cenarth, also in Carmarthenshire, and by Llandyfriog in Ceredigion. Adpar is the part of town on the Ceredigion side of the River Teifi. It was formerly called Trefhedyn and was an ancient Welsh borough in its own right.