Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.
BARCLAY
As described in historical dictionaries
An Etymological Dictionary of Family and Christian Names (1857)
(origin: Sax. Local) A corruption of Berkeley; a town in Gloucestershire, England, derived from the Saxon beorce, a beech-tree, and leagh or ley, a field, and so called because of the plenty of beech-trees growing there.
Patronymica Britannica (1860)
BARCLAY. We find a Theobald de Berlceley, probabi}' an offshoot of the English family, settled in Scotland, so early as temp. David I. Fourth in descent from him Avas Alex, de B., who married the heiress of Mathers, and wrote himself De Berkeley of Slathers. His great grandjou Alex, clianged the spelling to Barclay in the XV. century. Geneal. Ace. of Barclays of Ury.
Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
Origin: Celtic
Region of origin: British Isles
Country of origin: Scotland
Religion of origin: Christian
Language of origin: Gaelic