Llandeilo is a town and community in Carmarthenshire, Wales, situated where the River Towy is crossed by the A483 on a 19th-century stone bridge. At the 2021 census the community had a population of 1,784. It is adjacent to the westernmost point of the Brecon Beacons National Park. The town is served by Llandeilo railway station on the Heart of Wales Line.