Dumnonia is the Latinised name for the Brythonic kingdom in Sub-Roman Britain between the late 4th and late 8th centuries, in what is now the more westerly parts of South West England. It was centred in the area later called Devon, but included modern Cornwall and part of Somerset, with its eastern boundary changing over time as the gradual westward expansion of the neighbouring Anglo-Saxon kingdom of Wessex encroached on its territory. The spelling Damnonia is sometimes encountered, but is also used for the land of the Damnonii, later part of the Kingdom of Strathclyde (itself sometimes referred to as Damnonia), in what is today southern Scotland. Domnonia occurs as well, infrequently.

Dumnonia is the Latinised name for the Brythonic kingdom in Sub-Roman Britain between the late 4th and late 8th centuries, in what is now the more westerly parts of South West England. It was centred in the area later called Devon, but included modern Cornwall and part of Somerset, with its eastern boundary changing over time as the gradual westward expansion of the neighbouring Anglo-Saxon kingdom of Wessex encroached on its territory. The spelling Damnonia is sometimes encountered, but is also used for the land of the Damnonii, later part of the Kingdom of Strathclyde (itself sometimes referred to as Damnonia), in what is today southern Scotland. Domnonia occurs as well, infrequently.