In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Sennen like this:
SENNEN, a village and a parish in Penzance district, Cornwall. The village stands 387 feet above sea-level, 1 mile E of Lands-End, and 9 S W of Penzance r. station; and has an inn, called the First and Last inn in England. The parish includes Lands-End and the light-house off it; and comprises 2, 230 acres of land, and 70 of water. ...
Post-town, Penzance. Real property, £2, 887. Pop., 613. Houses, 123. The property is divided among a few. Salt-works were here at Domesday, but have been discontinued. Small harbours are at S. cove and Whitsand bay; and fishing is largely carried on. Roman coins were found in 1807. The living is a rectory in the diocese of Exeter. Value, £230. Patron, the Prince of.wales. The church is ancient but good. There are chapels for Baptists, Wesleyans, Primitive Methodists, and Bible Christians, and a national school.
GB Historical GIS / University of Portsmouth, History of Sennen, in Penwith and Cornwall | Map and description, A Vision of Britain through Time.
Date accessed: 25th April 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 " Sennen ".