Newcastle Emlyn is a town and community on the River Teifi, in West Wales. The community is wholly in Carmarthenshire, but the built up …Newcastle Emlyn is a town and community on the River Teifi, in West Wales. The community is wholly in Carmarthenshire, but the built up area also includes Adpar north of the Teifi, which is in Ceredigion. Adpar was formerly called Trefhedyn and was historically a borough in its own right. Newcastle Emlyn grew around its castle, which dates from the 13th century. At the 2021 census the community had a population of 1,144. The built up area had a population of 1,883 at the 2011 census.