In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Llangynfelyn like this:
LLANCYNFELIN, or LLANGYNVELIN, a parish in Aberystwith district, Cardigan; on the river Dyfi near its mouth, and on the Aberystwith and Welsh coast railway, near Ynys-Las r. station, 7 miles NNE of Aberystwith. It contains the village of Tre-Talyasin; and its Post town is Aberystwith. Acres, 6,556; of which 1,535 are water. ...
Real property, £2,432. Pop., 967. Houses, 216. The property is subdivided. Traces exist of Wyddno Castle, which belonged to Gwyddno Gwranhir, who was said to have lost a large tract of land here by inundation of the sea. Tre-Talyasin is believed to have been the burial-place of a famous bard; and a cairn at it, on rising-ground, is about 135 feet in circuit, and has in its centre the cistvaen or grave. Coal, limestone, marble, iron ore, and lead ore are worked. The living is a p. curacy in the diocese of St. Davids. Valne, £90. Patron, J. P. B. Chichester, Esq. The church is plain but good; is believed to occupy the site of one built in the 6th century; and is dedicated to St. Cynfelin.
GB Historical GIS / University of Portsmouth, History of Llangynfelyn, in Ceredigion and Cardiganshire | Map and description, A Vision of Britain through Time.
Date accessed: 28th March 2017
Click here for more detailed advice on finding places within A Vision of Britain through Time , and maybe some references to other places called " Llangynfelyn ".