Cornouaille is a historic region in Brittany, in northwest France. The name is the French equivalent for the Cornwall region of Britain. This can be explained by settlement of Cornouaille by migrant princes from Cornwall and the founding of the Bishopric of Cornouaille by ancient Saints from the Cornwall region. The two regions spoke a similar celtic language which evolved into the Cornish language in Britain, and into a similar language, the Breton language across the English Channel in Brittany; both Breton and Cornish in turn are similar to Welsh.

Cornouaille was established in the early Middle Ages in the southwest of the Breton peninsula. During this same period other British migrants established the region of Dumnonia (in Latin) or Domnonée (in French) in the north of the peninsula, taken from the British county of Devon derived from the Latin Dumnonia.

The region was first mentioned by this name between 852 and 857 when the Bishop of Saint-Corentin, Anaweten, took over "Cornugallensis". The name Cornwallis or Corn-wealas is from the name of Celtic tribe, Latinized as Cornovii, meaning "peninsula people", (from the Celtic "kernou", meaning "horn" or "headland". A cognate of the English "horn", both being from PIE *ker- "uppermost part of the body, head, horn, top, summit") with the suffix "-wealas", from "walh", a word used by the Germanic speakers, such as the English, for "a non-Germanic foreigner" especially a "Celtic speaker" but also used for Romance speakers (and is the element found in Walloon, Wales, Walachia, walnut, Wallace and Walsh). The name was used in reference to the resettling of the Celts from 'Great Britain' as opposed to 'Lesser Britain', the difference between 'La Grande Bretagne' – Great Britain – and 'La Bretagne', Brittany.