In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Undy like this:
UNDY, a parish in Chepstow district, Monmouth; on the South Wales railway and on the coast, 1 mile E of Magor r. station, and 7¼ WSW of Chepstow. Post town, Magor, under Chepstow. Acres, 3,717; of which 2,000 are water. Real property, £2,653. Pop., 411. Houses, 78. The property is divided among a few. The living is a vicarage in the diocese of Llandaff. Value, £183.* Patrons, the Dean and Chapter of L. 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 Undy 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 Undy and units named after it.
GB Historical GIS / University of Portsmouth, History of Undy in Monmouthshire | Map and description, A Vision of Britain through Time.
Date accessed: 24th May 2013
Click here for more detailed advice on finding places within A Vision of Britain through Time, and maybe some references to other places called "Undy".