In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Cwmyoy like this:
CWMYOY, a parish in the district of Abergavenny, and counties of Monmouth and Hereford; on the river Honddu, under the Black mountains, 2¾ miles NW of Llanfihangel r. station, and 6½ N of Abergavenny. It contains the hamlets of Fwthog and Bwlch-Trewyn, and the abbey of Llanthouy; and its post town is Llanfihangel-Crucorney, under Abergavenny. Acres, 10, 366. Real property, £3, 303. Pop., 649. Houses, 143. The property is divided among a few. The surface includes grand mountain and glen scenery. The living is a vicarage in the diocese of Llandaff. Value, £68. Patron, John Morgan, Esq. The church is good.
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 Cwmyoy has changed, please see our redistricted information for the modern district of Monmouthshire. More detailed statistical data are available under Units and statistics, which includes both administrative units covering Cwmyoy and units named after it.
GB Historical GIS / University of Portsmouth, History of Cwmyoy in Monmouthshire | Map and description, A Vision of Britain through Time.
Date accessed: 21st April 2015
Click here for more detailed advice on finding places within A Vision of Britain through Time, and maybe some references to other places called "Cwmyoy".