County town of Devon (6)
I believe the answer is:
exeter
'county town of devon' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for exeter that I've seen before include "The modern Isca Dumnoniorum" , "West Country cathedral city" , "City at S. end of M five" , "Oxford college; city" , "South-western English city" .)