Arthur, William (1857) An Etymological Dictionary of Family and Christian Names. New York: Sheldon, Blakeman. Public Domain.
ISHAM
As described in historical dictionaries
An Etymological Dictionary of Family and Christian Names (1857)
(origin: Local) Isis-ham, that is, the town on the river Isis, in Northamptonshire, England.
Patronymica Britannica (1860)
ISHAM. A place in the hundred of Orlingbui-y, co. Northampton, -where an elder branch of the existing family, Isham of Lamport, were seated soon after the Conquest. Shirley's Noble and Gentle Men.
Lower, Mark A (1860) Patronymica Britannica: a dictionary of the family names of the United Kingdom. London: J.R. Smith. Public Domain.
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