Straightforward Irish county? Correct (9)
I believe the answer is:
downright
'straightforward' is the definition.
(synonyms)
'irish county? correct' is the wordplay.
'irish county?' becomes 'Down' (County Down).
'correct' becomes 'right' (right can mean correct).
'down'+'right'='DOWNRIGHT'
(Other definitions for downright that I've seen before include "Completely" , "Utter, complete" , "Utter, arrant" , "Frank" , "Plain-spoken" .)