Has the English county of Devon ever had its own language, like Cornwall has Cornish?

The Devon accent(s) (there are differences between Devon's regions) have the westcountry 'burr' that is common to much of south-west Britain. What is perhaps less well known is that Devon was one of the last places to speak the Celtic language in what is now England. That language is similar to what is now known as Cornish and Breton. Whilst Cornish was spoken in Cornwall until almost the modern day and Breton is still spoken by many thousands, common use of the language is reputed to have died out in Devon in the middle ages. Books on the ancient Devon Brythonic language do exist (for example - an excellent booklet by linguist Joseph Biddulph exists entitled 'A Handbook of West Country Brythonic' (Old Devonian) [ISBN 1 897999 06 2] which can be ordered from the author)

However the language didn't simply die - it remains in numerous place names and surnames (such as Dew or Cann), and a number of words have been retained in Devon dialect.