Colchester's county (5)
I believe the answer is:
essex
'colchester's county' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for essex that I've seen before include "Home county" , "Eastern county" , "County NE of London" , "Stereotypical promiscuous and materialistic young woman (from Colchester?)" , "County near London" .)