Cornish surnames are surnames used by Cornish people and often derived from the Cornish language. Such surnames for the common people emerged in the Middle Ages, although the nobility probably had surnames much earlier on. Not until the later Middle Ages did it become necessary for a common man to have a surname. Most surnames were fully established throughout Cornwall by the end of the 15th century. Today Cornish surnames can be found throughout the world as part of the Cornish diaspora.
Due to the linguistic similarity of Cornish, Welsh and Breton, some surnames can derive from any of the three regions.
The commonest surnames in Cornwall are derived from patronymics, the father’s first name being taken either without alteration, for example 'John', or with the addition of genitive '-s' or, typically Cornish, '-o', e.g. 'Bennetto' or '-y' as in 'Pawley'.
The phrase Tre, Pol and Pen is used to describe people from, or places in, Cornwall, the United Kingdom. Carew has By Tre, Pol and Pen / You shall know the Cornishmen; however, Camden records the rhyme as By Tre, Ros, Pol, Lan, Caer and Pen / You may know the most Cornishmen.
Many Cornish surnames and place names still retain these words as prefixes, such as the names Trelawny or Trevithick and the towns of Polperro, Polkerris and of course Penzance. "Carbines" derives from karn byghan "little tor".
Caution should be exercised with the derivation of "Car-" surnames as there seems also to be fusion with names containing the word ker "hill-fort", as in "Carvosso" ker fosow "walled hill-fort", a placename found in Ludgvan. There is also karrek "rocky". "Rosdew" is ros du "black moor" and "Ros(e)warne" from ros (g)wern "alder heath" or perhaps "heath by an alder-marsh". "Landry" means lan dre "enclosure of farmhouse or church-house".