Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.
THROCKMORTON
As described in historical dictionaries
An Etymological Dictionary of Family and Christian Names (1857)
A corruption of At Rock-moor-town, "a town on a rock in a moor," in the vale of Evesham, Fladbury, Warwickshire, England, whence the name was derived.