The Kingdom of Cornwall is an independent polity in southwest Britain during the Early Middle Ages, roughly coterminous with the modern county of Cornwall.

During the sub-Roman and early medieval periods Cornwall was evidently part of the kingdom of Dumnonia, which included most of the West Country, but the exact nature of its relationship with the kingdom is unclear.

Between the 7th and the 10th centuries most of Dumnonia's land is gradually taken by the Anglo-Saxon kingdom of Wessex, and Cornwall emerges as a rump state known to the Saxons as West Wales.

Cornwall is not conquered by the Anglo-Saxons but rather it is co-opted into the Anglo-Saxon crown; by the reign of Edward the Confessor (1042–1066) it is part of the Earldom of Wessex.

Since then, the titles Earl of Cornwall and Duke of Cornwall have been used by the English peerage, beginning in the reign of William the Conqueror.