Devonshire, which occupies rather more than one-twenty-second of the whole area of England and Wales, is one of the largest counties in the British Islands, being exceeded in size only by Yorkshire and Lincoln in England, by Inverness and Argyll in Scotland, and by Cork in Ireland. Its extreme length from east to west, measured along a horizontal line drawn through the middle of the county, starting at the Dorsetshire border half-way between Lyme Cobb and the Seven Rocks Point, passing close to the city of Exeter, and reaching to the point where the river Ottery enters the county, is 67 miles; exactly the same as that of the county of Somerset. Its greatest breadth, from Countisbury Foreland on the north coast to Prawle Point on the south, is 71 miles. It may be added that a longer east and west line can be drawn only in Yorkshire and Sussex, and a longer meridional line only in Yorkshire and Lincoln. The area of the "Ancient" or "Geographical" county of Devonshire, according to the revised return furnished by the Ordnance Department, is 1,667,154 acres, or 2605 square miles. Compared with the counties that adjoin it, it is two-and-a-half times the size of Dorset, it is roughly twice as large as Cornwall, and it is more than half as large again as Somerset. It is fifteen times as large as Rutland, it is about half the size of Yorkshire, and its area is less than that of Lincolnshire by only 48 square miles.

Glen Lyn, near Lynmouth

Although usually said to be irregular in form, the outline of the county has a certain degree of symmetry, being roughly shaped like a life-guardsman's cuirass, with nearly equal sides, with a small hollow at the top or north coast, and a much larger one at the bottom or south coast.

Devonshire, like Kent and Cornwall, is bounded on two sides by the sea, having the Bristol Channel on the north and north-west, and the English Channel on the south. On its western side the river Tamar, with its tributary the Ottery, forms almost the whole of the frontier between it and Cornwall. The eastern and north-eastern border is less definite, but is roughly marked by Exmoor and the Blackdown Hills, which partly separate Devonshire from Somerset. The short length of frontier between Devonshire and Dorsetshire is marked by no natural feature.

No part of Devonshire is now, as was formerly the case, wholly surrounded by any other county. Three of its parishes, however, are partly in Dorset, one is partly in Cornwall, and one, a district of Exmoor containing no houses or inhabitants, is partly in Somerset. Culmstock, which before 1842 was considered to belong to Somerset, although completely islanded in Devon, and Stockland and Dalwood, which were reckoned with Dorset, although they were entirely inside the Devonshire border, have now been formally transferred to this county. On the other hand, Thornecombe and Ford Abbey, which belonged to Devonshire although they were situate in the adjoining county, have been handed over to Dorset. Still later alterations were the transfer of Hawkchurch and Churchstanton from Dorset to Devon in 1896.