It lies between Rhondda and the Merthyr Valley and takes its name from the River Cynon.

[citation needed] From 1974 to 1996, the borough of Cynon Valley was one of thirty-seven districts of Wales.

[5] It was one of six districts of Mid Glamorgan, and in 1996 was merged into the larger unitary authority of Rhondda Cynon Taf.

[7][8][9] In 1983, the parliamentary constituency of Cynon Valley was formed for the election of a member of parliament to the House of Commons.

In 2010, the constituency was redefined as consisting of 15 electoral divisions of the county borough of Rhondda Cynon Taf: Aberaman North, Aberaman South, Abercynon, Aberdare East, Aberdare West/Llwydcoed, Cilfynydd, Cwmbach, Glyncoch, Hirwaun, Mountain Ash East, Mountain Ash West, Penrhiwceiber, Pen-y-waun, Rhigos, Ynysybwl.