Merthyr Tydfil County Borough is a county borough in the south-east of Wales. In 2022, it had an estimated population of 58,883, making it the smallest local authority in Wales by population. It is located in the historic county of Glamorgan and takes its name from the town with the same name. The county borough consists of the northern part of the Taff Valley and the smaller neighbouring Taff Bargoed Valley. It borders the counties of Rhondda Cynon Taf to the west, Caerphilly County Borough to the east, and Powys to the north. The area was awarded county borough status in 1908 until the original county borough was abolished in 1974. In 1996, Merthyr Tydfil became a principal area and one that is styled as a "county borough" in recognition of its historical status.