Cornwall (;Cornish: Kernow [ˈkɛrnɔʊ]) is a ceremonial county in South West England. It is recognised as one of the Celtic nations and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, with the River Tamar forming the border between them. Cornwall forms the westernmost part of the South West Peninsula of the island of Great Britain. The southwesternmost point is Land’s End and the southernmost Lizard Point. Cornwall has a population of 568,210 and an area of 3,563 km2 (1,376 sq mi). The county has been administered since 2009 by the unitary authority, Cornwall Council. The ceremonial county of Cornwall also includes the Isles of Scilly, which are administered separately. The administrative centre of Cornwall is Truro, its only city.
Cornwall was formerly a Brythonic kingdom and subsequently a royal duchy. It is the cultural and ethnic origin of the Cornish diaspora. The Cornish nationalist movement contests the present constitutional status of Cornwall and seeks greater autonomy within the United Kingdom in the form of a devolved legislative Cornish Assembly with powers similar to those in Wales, Scotland and Northern Ireland. In 2014, Cornish people were granted minority status under the European Framework Convention for the Protection of National Minorities, giving them recognition as a distinct ethnic group.
Few Roman remains have been found in Cornwall, and there is little evidence that the Romans settled or had much military presence there. After the collapse of the Roman Empire, Cornwall (along with Devon, parts of Dorset and Somerset, and the Scilly Isles) was a part of the Brittonic kingdom of Dumnonia, ruled by chieftains of the Cornovii who may have included figures regarded as semi-historical or legendary, such as King Mark of Cornwall and King Arthur, evidenced by folklore traditions derived from the Historia Regum Britanniae. The Cornovii division of the Dumnonii tribe were separated from their fellow Brythons of Wales after the Battle of Deorham in 577 AD, and often came into conflict with the expanding English kingdom of Wessex. The regions of Dumnonia outside of Cornwall (and Dartmoor) had been annexed by the English by 838 AD.King Athelstan in 936 AD set the boundary between the English and Cornish at the high water mark of the eastern bank of the River Tamar. From the Early Middle Ages, language and culture were shared by Brythons trading across both sides of the Channel, resulting in the corresponding high medieval Breton kingdoms of Domnonée and Cornouaille and the Celtic Christianity common to both areas.