Tom's about to go round Irish county (8)
I believe the answer is:
somerset
'county' is the definition.
(I've seen this before)
'tom's about to go round irish' is the wordplay.
'about' is an anagram indicator.
'to go round' indicates putting letters inside.
'irish' becomes 'erse' (I've seen this before).
'toms' anagrammed gives 'somt'.
'somt' enclosing 'erse' is 'SOMERSET'.
(Other definitions for somerset that I've seen before include "Street location" , "head over heels" , "leap, occasionally" , "... and another" , "part of the west" .)