In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Sealand like this:
SEALAND, a township in Hawarden parish, Flint; 2 miles N W of H. village. Acres, 5, 514; of which 535 are water. Real property, £6,052. Pop. in 1851, 291; in 1861, 390. Houses, 66. The increase of pop. arose from reclamation of marsh land. A church was built here in 1866, and is in the early English style.
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 Sealand has changed, please see our redistricted information for the modern district of Flintshire. More detailed statistical data are available under Units and statistics, which includes both administrative units covering Sealand and units named after it.
GB Historical GIS / University of Portsmouth, History of Sealand in Flintshire | Map and description, A Vision of Britain through Time.
Date accessed: 20th February 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 "Sealand".