LLANTHETTY is also referred to a Llanddetty - Extract from National Gazetteer, 1868
[Description(s) from The National Gazetteer (1868)]
"LLANTHETTY, a parish in the hundred of Pinkelly, county Brecon, 7 miles S.E. of Brecknock, its post town. It is situated on the Roman Via Julia Montana and the river Usk. The Brecon canal passes through the parish, which includes the townships of Dyffrin and Taf-Vechan. The living is a rectory* in the diocese of St. David's, value 344. The parish church is dedicated to St. Detta. There is also the district church of Taf-Vechan, a perpetual curacy, in the gift of the rector. Here are several good residences, the principal being Llanthetty Hall."
"DYFFRIN, a hamlet in the parish of Llanthetty, hundred of Penkelly, in the county of Brecon, 6 miles N.W. of Crickhowel. It is situated near the canal and the river Usk. Its name, Dyffrin, or Dyffryn, is derived from dyfcr hynt, a watercourse in a wide vale."

"TAL-Y-BONT, a village in the parishes of Llanthetty and Llanvigan, county Brecon, 5 miles S.E. of Brecknock."

"VRO, a parcel in the parish of Llanthetty, hundred of Penkelly, county Brecon. It is situated near the Usk and Brecon canal, and includes Tal-y-bont."

[Description(s) from The National Gazetteer of Great Britain and Ireland (1868)Transcribed by Colin Hinson 2003]