In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Blackmanstone like this:
BLACKMANSTONE, a parish in Romney-Marsh district, Kent; 5 miles ESE of Ham-street r. station. Post-stown, New Romney. Acres, 293. Real property, £825. Pop., 8. Houses, 2. The living is a rectory in the diocese of Canterbury. Value, £44. Patron, the Archbishop.
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 Blackmanstone has changed, please see our redistricted information for the modern district of Shepway. More detailed statistical data are available under Units and statistics, which includes both administrative units covering Blackmanstone and units named after it.
GB Historical GIS / University of Portsmouth, History of Blackmanstone, in Shepway and Kent | Map and description, A Vision of Britain through Time.
Date accessed: 08th October 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 "Blackmanstone".