In 1870-72, John Marius Wilson's Imperial Gazetteer of England and Wales described Lopen like this:
LOPEN, a parish, with a village, in Chard district, Somerset; 2 miles S by E of South Petherton, and 4 NNW of Crewkerne r. station. Post town, South Petherton, under Ilminster. Acres, 489. Real property, £2,145. Pop., 419. Houses, 99. The property is subdivided. The manor belongs to Earl Poulett. The living is a vicarage in the diocese of Bath and Wells. Value, £96. Patron, Earl Poulett. The church is ancient but good; was enlarged in 1834; and comprises transept and chancel, with bell-turret.
GB Historical GIS / University of Portsmouth, History of Lopen in South Somerset | Map and description, A Vision of Britain through Time.
Date accessed: 23rd March 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 " Lopen ".