Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
DOWN
As described in historical dictionaries
Patronymica Britannica (1860)
DOWNE. DOWN. A-Sax. dm, a hill, as the South Downs, Marlborough Downs, &c. From residence in such a locality have come the surnames Downe, Downer, Downman, Downes, &c. The H.R. form is Ate-Dune, i.e. ' At the Down.'
Surname type: Location or geographical feature
Origin: English
Region of origin: British Isles
Country of origin: England
Religion of origin: Christian
Language of origin: English