Hen Dy Cwrdd Unitarian Chapel was built in 1751 as a cottage-like meeting house and was originally known as Ty Cwrdd Godre Hirwaun. Described as the Mother Church of Unitarianism in the Cynon Valley, it was the first place of worship in the valley, originating from Dissenter meeting houses at Cwmyglo and Blaencaniad Farm. However it is unclear at what date the chapel became Unitarian, theories suggesting that the original chapel was a Calvinistic split due to theological differences to Cwmyglo, and became Unitarian only in 1813 when the Unitarians finally split from the Established church.

The chapel was built in a field belonging to the old farm of Gadlys Uchaf, the lease granted on the 5th March 1751 by Theophilus Richards and revised by his son Richard Richards on 12th December 1796. The original building was small and simple, described as having a porch etrance with outside stone steps and a tiled roof. Accommodating 50-100 people, in 1782 there were 43 members, by 1853 it was 60. The chapel was rebuilt in 1862 at a cost of £753-15s-4d to the design of architect Evan Griffiths of Aberdare, designed to be "simple and strong, reflecting Unitarian beliefs in liberty, tolerance and forbearance".

The symmetrical cement rendered front is built in the Italianate style with a gable-entry plan. The bottom half of the facade is channelled, with a round arched doorway to the centre which has stone steps up to panelled double doors. Above is the inscribed stone plaque, while to either side are square-headed sash windows. At gallery level is a pair of round-headed windows over which arches the moulded stringcourse, and to either side are two further sash windows, those to the centre narrower than the outer openings. In the pediment is a round attic window.

The square interior has a pulpit at the rear wall, accessed to either side by steps from the Sedd Fawr and with an arched recess behind. A gallery runs round three sides, supported by cast iron columns and with an unusually deep gallery front. th ceiling has a simple cornice, a central rose and octagonal ventilation panels.

Hen Dy Cwrdd is now Grade II Listed and is in the ownership of the Welsh Religious Buildings Trust.

Hen dy Cwrdd also ran the Trecynon Seminary, once famous for its education.

RCAHMW, April 2010

Dr Jacob Dafis (ed), Crefydd a Gweriniaeth yn hanes Yr Hen-dy-Cwrdd, Aberdare l75l-l951, (Gomer Press, Llandyssul, 1951).
The Unitarian Heritage, 1986, p 11
R Jenkins Jones 'The Origin and History of the old meeting House, Hen-dy-Cwrdd
Aberdare' Transactions of the Unitarian History Society, Vol 1 pt 2 (1918) p 155-176.
Alan Vernon Jones, Chapels of the Cynon Valley (Cynon Valley History Society, 2004)