In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Llanarmon Mynydd Mawr like this:
LLANARMON-MYNYDD-MAWR, a parish in the district of Llanfyllin and county of Denbigh; adjacent to Montgomeryshire, 3½ miles SSW of Llanarmon-DyffrynCeiriog, and 6 N of Llanfyllin r. station. Post town, Llanfyllin, under Oswestry. Acres, 2,590. Real property, with Banhadla-Ucha and Henfache, £2,471. Rated property, of L. alone, £844. Pop., 140. Houses, 25. The property is divided among a few. The living is a p. curacy in the diocese of St. Asaph. Valne, £64. Patron, the Bishop of St. Asaph. The church is tolerable.
A Vision of Britain through Time includes a large library of local statistics for administrative units. For the best overall sense of how the area containing Llanarmon Mynydd Mawr has changed, please see our redistricted information for the modern district of Powys. More detailed statistical data are available under Units and statistics, which includes both administrative units covering Llanarmon Mynydd Mawr and units named after it.
GB Historical GIS / University of Portsmouth, History of Llanarmon Mynydd Mawr, in Powys and Denbighshire | Map and description, A Vision of Britain through Time.
Date accessed: 30th May 2016
Click here for more detailed advice on finding places within A Vision of Britain through Time, and maybe some references to other places called "Llanarmon Mynydd Mawr".