Devon (/ˈdɛvən/), also known as Devonshire, which was formerly its common and official name, is a county of England, reaching from the Bristol Channel in the north to the English Channel in the south. It is part of South West England, bounded by Cornwall to the west, Somerset to the northeast, and Dorset to the east. The City of Exeter is the county town; seven other districts of East Devon, Mid Devon, North Devon, South Hams, Teignbridge, Torridge, and West Devon are under the jurisdiction of Devon County Council; Plymouth and Torbay are each a part of Devon but administered as unitary authorities. Combined as a ceremonial county, Devon's area is 6,707 km² (2,590 square miles) and its population is about 1.1 million.

Devon derives its name from Dumnonia, which, during the British Iron Age, Roman Britain, and Early Medieval was the homeland of the Dumnonii Brittonic Celts. The Anglo-Saxon settlement of Britain resulted in the partial assimilation of Dumnonia into the Kingdom of Wessex during the eighth and ninth centuries. The western boundary with Cornwall was set at the River Tamar by King Æthelstan in 936. Devon was constituted as a shire of the Kingdom of England thereafter.