Hi Nigel
The Cilgwyn you are interested in shouldn't be confused with either the golf course, or the mansion. I don't think it is the oldest cause in Wales either, Llanvaches and others are older - but pretty old nevertheless.
Cilgwyn, where the dissenting cause met - for safety presumably - was CILGWYN UCHAF, Llangybi ie the upper of the two farms called CILGWYN (the other is Cilgwyn Isaf), which is on the same narrow road out of the village.
There wasn't a graveyard at the farm - or I have never heard of one - there is now no sign of the old days there, except (as the farmer tells me) that when ploughing you can feel the unevenness of the land.
There is a narrow lane above Cilgwyn Ucha' above a cleft in the land where a stream runs. I have been told that the preacher would stand on one side of the small ravine, and the congregation on the other...
There was a split from Cilgwyn in the 1700s, as members who objected to the heresies of the original group (ie they disagreed, basically, over interpretations of the Trinity and the means of achieving Salvation) decamped down the road to Llangybi village, where they have met ever since - this is the Congregationalist Chapel (Annibyniol) - Capel Ebenezer.
Later Cilgwyn moved down to the village as well. The old Cilgwyn chapel book (now lost) apparently related that they took all the stones from the original meeting house, together with the larch trees, and built a new chapel - still standing, but now unused, in the village.
There was a further split from Cilgwyn (who became Wesleyan Methodist) by the Calvinistic Methodists - who built yet another chapel just down the road. At one stage within two miles of each other there were four chapels (the other was Beddyddwr - Baptists) and two churches.
People - members of the other chapels nearby - who still live in the village remember fondly the Cwrdd Nos (evening meeting) which was held once a month in Cilgwyn chapel. The old Cilgwyn graveyard is still with the chapel in the centre of the village. The details of the stones inscriptions are in the book I have given details of below.
On line there are some of the Baptismal entries in the Cilgwyn records -
http://freepages.genealogy.rootsweb.ancestry.com/~hughwallis/IGIBatchNumbers/CountyCardigan.htm#PageTitleCilgwyn Chapel Llangybi 1770-1878
For records of monumental inscriptions see the James's fantastic work in
Beddargraffiadau A Mynegion (Monumental Inscriptions and Indexes)
Vol XV Gartheli Area - which includes the gravestones of Cilgwyn.
This is in the National Library of Wales Aberystwyth - and also, I believe, in Aber. Public Library.
I hope you find this helpful.
Cheers
Jen