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.
Origin of name 
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.
Strong contacts between Armorica (a larger region than the Duchy of Brittany or modern Brittany) and southern Britain had already been noted by Julius Caesar. Native British troops were hired to support the usurpation of Magnus Maximus, who is said to have settled them in Armorica. Settlements expanded when Anglo-Saxon invaders expanded westward within Britain. Strong links existed in the 6th century between the British and Armorican territories. Arthurian legends make frequent reference to the maritime connections between the peoples of Wales, southern Ireland, Cornwall in southwestern Britain and the early kingdoms of Brittany, cf. the tale of Tristram and Yseult.
The existence of an ancient district in Anjou called "La Cornuaille" has led to the hypothesis that Cornouaille may have been a geographical or military label for all of southern Brittany as far as the northern shore of Domnonée in the 6th or 7th century.
The name Cornouaille signifies the diocese of Quimper which persisted until the French Revolution. The diocese covered more than half of the south of Finistère, and extended over part of Morbihan and the Côtes-d'Armor. There were two arch-deacons, one for Cornouaille and one for Poher. There were also a cantor, a treasurer, a theologian and twelve canons. This episcopal division was the poorest in Brittany.
List of rulers 
- Judicael (circa 857-874) - the county of Cornouaille is not yet precisely defined. Its leaders represent the interests of "western Brittany" and join the King of Brittany in fights against the Vikings.
- Riwallon (circa 874)
- Gourmaëlon (early 10th century)
- Alan II (early to mid-10th century)
- Alain Canhiart
- Hoel of Cornouaille, who ruled Brittany as Duke jure uxoris.
- Alan IV
- Isaac Taylor, Names and Their Histories: A Handbook of Historical Geography and Topographical Nomenclature, BiblioBazaar, LLC, 2008, p.70
- "Cornwall". Online Etymology Dictionary. Retrieved 2013-05-21.
- "Horn". Online Etymology Dictionary. Retrieved 2013-05-21.
- "Welsh". Online Etymology Dictionary. Retrieved 2013-05-21.
- Léon Fleuriot, Les origines de la Bretagne, Éd. Payot, 1980