Gosh: new boundary for county (8)
I believe the answer is:
cornwall
'county' is the definition.
(I know that Cornwall is a county)
'gosh new boundary' is the wordplay.
'gosh' becomes 'cor' (I've seen this before).
'new' becomes 'n' (abbreviation as in New Testament NT).
'boundary' becomes 'wall' (a wall might act as a boundary).
'cor'+'n'+'wall'='CORNWALL'
'for' is the link.
(Other definitions for cornwall that I've seen before include "Crown all in the English county, strangely" , "hilly county" , "Part of 1 25 [KING LEAR]" , "Duchy" , "County of south-west England" .)