County band's back, or group (6)
I believe the answer is:
dorset
'county' is the definition.
(I've seen this before)
'band's back or group' is the wordplay.
'back' indicates one should take the final letters.
'group' becomes 'set' (set is a kind of group**).
The last letter of 'band' is 'd'.
'd'+'or'+'set'='DORSET'
(Other definitions for dorset that I've seen before include "County of south-west England" , "South-west area" , "part of England" , "A SW county" , "County adjoining 1" .)