English county providing cereal with everything (8)
I believe the answer is:
cornwall
'english county' is the definition.
(I've seen this before)
'cereal with everything' is the wordplay.
'cereal' becomes 'corn' (corn is a kind of cereal).
'with' becomes 'w' (abbreviation).
'everything' becomes 'all' (all things).
'corn'+'w'+'all'='CORNWALL'
'providing' acts as a link.
(Other definitions for cornwall that I've seen before include "County in southwestern England" , "Southwestern English county" , "Land" , "hilly county" , "Southern English county" .)