Cefn-coed-y-cymmer is a small community on the northwestern edge of Merthyr Tydfil County Borough in Wales. It is situated in the neck of land between the rivers Taf Fawr and Taf Fechan at their confluence. The village lies within the community of Vaynor. Immediately to the north of the village is the hill of Cefn Cil Sanws on the southern slopes of which is Merthyr Tydfil Golf Club. The village is bounded both to the north and the west by the Brecon Beacons National Park.

Merthyr Tydfil County Borough is a county borough in the south-east of Wales. In mid 2018, it had an estimated population of 60,183 making it the smallest local authority in Wales by both population and land area. 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.