Its principal towns are - Aberdare, Llantrisant with Talbot Green and Pontypridd, with other key settlements/towns being - Maerdy, Ferndale, Hirwaun, Llanharan, Mountain Ash, Porth, Tonypandy, Tonyrefail and Treorchy.

[5] The county borough was formed on 1 April 1996 under the Local Government (Wales) Act 1994, 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).

Many of the roads are lined with semi-ribbon development of closely packed Victorian terraces of houses which have given the Rhondda and Cynon valleys their distinctive appearance.

The coal industry has had major adverse impacts on the quality of the environment, such that most of the rivers were severely polluted to the exclusion of all fish life.

The chemical industry has also had adverse effects due to the dumping of toxic waste in the now disused Brofiscin Quarry in the village of Groes-faen.

A Dr Papageorge, formerly Monsanto's chief scientist, estimates that between 60,000 and 80,000 tonnes of polychlorinated biphenyl (PCB) contaminated wastes were dumped there.

[10] Works costing £1.25 million to reduce health risks to local residents and members of the public using a nearby footpath were completed at the quarry in 2012.