Five score in county division (7)
I believe the answer is:
hundred
I believe this is a double definition.
'five score' is the first definition.
(five twenties)
'county division' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for hundred that I've seen before include "Old subdivision of a shire or county" , "See 19" , "Historical division of a county - number" , "Number - old part of a shire" , "part of Chilterns maybe" .)