[1] It includes the districts and villages of Cefnpennar, Cwmpennar, Caegarw, Darranlas, Fernhill, Glenboi and Newtown, all within the historic county boundaries of Glamorgan.

Contemporary tithe maps even show that the early village is named Dyffryn, despite the river mouth being in its immediate vicinity.

Although, both Aberpennar and Duffryn had continued usage in various forms, notably for roads, canals, hotels, railways and collieries.

Other late 19th century writers such as David Watkin Jones also used the name Mountain Ash even when writing exclusively in Welsh.

[7] The issue of the town's Welsh name was resolved when the National Eisteddfod was held at the grounds of Dyffryn House in 1905.

In the previous year, the Eisteddfod was announced in the Aberdare Leader with the publication of a Penillion Telyn (lyrics for harp) by the poet Watkin Wyn.

[9] The coal industry began to decline after the First World War, but after the Second, manufacturing was introduced to offset the serious fall in local employment.

One event on a Friday evening in late January came when a procession paraded through the main streets before a revivalist meeting at Bethania Chapel addressed by the Rev.

[14] By 1894 the local government district had been enlarged to cover parts of the civil parishes of Aberdare, Llanwonno, and Llanfabon.

[15] The council went on to build Mountain Ash Town Hall, completed in 1904, to serve as its offices and meeting place.

[20] The town is served by Mountain Ash railway station on the Aberdare branch of the Merthyr Line of the Transport for Wales Rail network.

Developed by Powell Duffryn as it consolidated various industrial assets, the railway started from Afon Cynon at the Penrikyber Colliery, headed north past a coal-stocking area at Pontcynon, then past an interchange yard known as Lansdale Yard, and through the former Nixon's Navigation colliery – home of the railway's central workshops, locomotive sheds and weighbridge – and on north past Duffryn Colliery, terminating at the Abercwmboi Phurnacite plant.

[21] The NCB were persuaded to donate the locomotive to National Museum Wales, which has since loaned it indefinitely to the Llangollen Railway.

Mountain Ash Comprehensive School caters for pupils aged 11–18, on the site of the former estate of Lord Aberdare.

The Rugby league club South Wales Scorpions played its home matches in Mountain Ash in the 2014-15 season.

Mountain Ash served as inspiration for the fictional town of Aberowen in Fall of Giants and the rest of the Century Trilogy written by Ken Follett.