Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
FENN
As described in historical dictionaries
Patronymica Britannica (1860)
FENN. A-Sax. feim, a marsh or bog. From residence near one. In old documents the forms are Atte Fenne, Del Fen, De Fen, De Fenne, &c., sometimes modified to Fenner,
Origin: English
Region of origin: British Isles
Country of origin: England
Religion of origin: Christian
Language of origin: English