Rhondda Cynon Taf, or RCT, is a county borough in the South Wales Valleys of Wales. It consists of 3 valleys: the Rhondda Valley, Cynon Valley, and Taff-Ely Valley. Results from the 2011 census showed 19.1% of its 234,410 residents self-identified themselves as having some ability in the use of the Welsh language.
The county borough borders Merthyr Tydfil and Caerphilly to the east, Cardiff and the Vale of Glamorgan to the south, Bridgend and Neath Port Talbot to the west and Powys to the north. Its principal towns are - Aberdare, Llantrisant with Talbot Green and Pontypridd, with other key settlements/towns being - Ferndale, Hirwaun, Llanharan, Mountain Ash, Porth, Tonypandy, Tonyrefail and Treorchy.
See List of places in Rhondda Cynon Taf for a list of towns and villages. The most populous town in Rhondda Cynon Taf is Aberdare with a population of 31,705 (2001 Census), followed by Pontypridd with 29,781.
The county borough was formed on 1 April 1996, by the merger of the former Mid Glamorgan districts of Rhondda, Cynon Valley and Taff-Ely (with the exceptions of Creigiau and Pentyrch, which were added to Cardiff). Its name reflects all these, and thus also the rivers Rhondda, Cynon and Taff.
The first three maps are provided by A Vision of Britain through Time
These maps were found on Wikimedia Commons
These maps of Glamorgan post-1974 were found on another site and are very useful for sorting out the up-to-date geography of the area