Cyfarthfa Castle (courtesy of Keith Willoughby)

Merthyr Tydfil is a county borough, which was formerly in the historic county of Glamorgan. The area of the Merthyr County Borough consists of the northern part of the Taff Valley and the smaller neighbouring Taff Bargoed Valley.

It is bordered by Caerphilly, Powys and Rhondda Cynon Taf. Its principal town is Merthyr Tydfil.