In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Llannarth like this:
LLANARTH, a parish in Aberayron district, Cardigan; on the rivulet Lethi or Llethy down to the coast; 4¼ miles SSW of Aberayron, and 13 WNW of Lampeter r. station. It has a post office under Carmarthen, and fairs on 12 Jan., 12 March, 17 June, 22 Sept., and the Wednesday after 12 Dec.; and it includes the hamlets of Dre, Fach, Gafriw, Gelli, Goytre, Hir, Llyffannog, Mochros, Talybonllwyd, and Werr. ...
Acres, 15,044; of which 25 are water. Real property, £6,034. Pop. in 1 851,2,337; in 1861,2,216. Houses, 524. The property is divided among a few. Noyadd-Llanarth beLonged formerly to the Gryffiths, and belongs now to Lord Kensington. Wern belonged, in the time of Henry VII., to the Lloyds; and gave entertainment to that monarch, on his way to Bosworth field. Ancient camps are at Pen-y-gaer and Castell-Moeddyn. The living is a vicarage, united with vicarage of Llanina, in the diocese of St. Davids. Value, £120. * Patron, the Bishop of St. Davids. The church consists of nave and chancel, with a massive tower; contains some curious monuments; and was in disrepair in 1866. An inscribed stone, bearing a cross, with four circular holes at the junction of the arms, and associated with a wild legendary story, was in the churchyard, and has been removed into the tower. A school, with capacity for about 120 children, was built in 1859, at a cost of £700; and is surmounted with a bellcott and a spirelet.
GB Historical GIS / University of Portsmouth, History of Llannarth, in Ceredigion and Cardiganshire | Map and description, A Vision of Britain through Time.
Date accessed: 23rd 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 " Llannarth ".