In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Llanbadarn Fawr like this:
LLANBADARN-FAWR, a parish in Rhayader district, Radnor; on the river Ithon, 7 miles NE of Newbridge-on-Wye r. station, and 8½ WNW of New Radnor. It is divided into the townships of Brinhyfedd and Cellws; and it contains the village of Penybont, which has a postoffice designated Penybont, Radnorshire. ...
Acres, 3,646. Real property, £2,708. Pop., 475. Houses, 79. The property is much subdivided. Penybont Hall is the seat of J.Severn, Esq. The living is a rectory in the diocese of St. David's. Value, £268. Patron, the Bishop of St. David's. The church has a S doorway of seemingly very early Norman work, with some curious carving in the tympanum; and is in good condition.
GB Historical GIS / University of Portsmouth, History of Llanbadarn Fawr, in Powys and Radnorshire | 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 " Llanbadarn Fawr ".