Worker on edge in Ulster county (6)
I believe the answer is:
antrim
'ulster county' is the definition.
(I've seen this before)
'worker on edge' is the wordplay.
'worker' becomes 'ant' (worker is a type of ant).
'on' says to put letters next to each other.
'edge' becomes 'rim' (rim is a kind of edge**).
'ant'+'rim'='ANTRIM'
'in' is the link.
(Other definitions for antrim that I've seen before include "Ulster county" , "County of Northern Ireland" , "Giant's Causeway county" , "County in Ireland's north-east" , "County of northeast Ireland" .)