In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Llanwddyn like this:
LLANWDDYN, a village and a parish in Llanfyllin district, Montgomery. The village stands on the river Bechan or Owddyn, 10 miles W by N of Llanfyllin r. station; and has a post office under Oswestry, and fairs on 8 May and 2 Oct.The parish contains the townships of Llan, Abermarchant, Garthbwlch, Rhiewargor, and Sputy. Acres, 20,190. Real property, £1,982 Pop., 529. Houses, 111. Most of the surface is moor and mountain. Slate is quarried. The living is a vicarage in the diocese of St. Asaph. Value, not reported.* Patron, the Earl of Powis.
GB Historical GIS / University of Portsmouth, History of Llanwddyn, in Powys and Montgomeryshire | Map and description, A Vision of Britain through Time.
Date accessed: 26th April 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 " Llanwddyn ".