Surnames came into use in the 12th and 13th centuries. In "A Dictionary of British Surnames" by P H Reeney the following entry is to be found:
'Cornish, Cornes, Badekoc Korneys 1296 SRsx;
John Corneys 1327 SRsf;
Henry Cornysh 1375 LoPleas
Cornish "a Cornish man" is first recorded in the National E Dictionary in 1547. There must have been a ME Cornish formed on the analogy of English which was usually Normanized as Corneys. Adam Corneys (1300 LoCt) is probably identical with Adam Le Cornwalais 1275 RH v Cornwallis.'
Some Crests which have been used by various branches of Cornish families.
People who left Cornwall were labelled "Cornish" so one would expect to find more of us Cornishes out of Cornwall than still living there! Indeed we are widely spread! However, all of us must have ancestors who originated from that beautiful rugged county (or country?). No doubt those who bear the name and live in Cornwall must have ancestors who left the county, acquired the name, and subsequently returned, or were much travelled.
Bob Brooking of "The Brooking Society" pointed out to me that other names given to people who left Cornwall include: Cornwall, Cornwell, Curnow, Cornu, Kernew, Kernow and the like. He rightly comments that it is possible that in previous centuries these names may have alternated. However, at present the Society is only concerned with the surname of CORNISH.
What can be said with certainty is that everyone of us with the name must have origins in the county of Cornwall although proving this is not an easy task, if at all possible.
Over the centuries the spelling of "Cornish" has varied. These are the variants I have found so far: Cornysshe, Cornyshe, Cornysh, Cornishe, Cornisshe, Cornis but on the whole all these have been standardised as "Cornish" today.