County briefly in the money (5)
I believe the answer is:
bucks
I believe this clue is a double definition.
'county briefly' is the first definition.
(short for Buckinghamshire; 'briefly' indicates a short form)
'the money' is the second definition.
(informal term for dollars)
'in' is the link.
(Other definitions for bucks that I've seen before include "County to northwest of London (abbrev.)" , "Opposes;, males" , "overseas money" , "Goes against" , "young men" .)