County associated with married show-off - a writer of music (8)
I believe the answer is:
composer
'a writer of music' is the definition.
(I've seen this before)
'county associated with married show-off' is the wordplay.
'county' becomes 'co'.
'associated with' says to put letters next to each other.
'married' becomes 'm' (abbreviation, e.g. in genealogy).
'show-off' becomes 'poser' (poser is a kind of show-off).
'co'+'m'+'poser'='COMPOSER'
(Other definitions for composer that I've seen before include "Person who writes music" , "eg Ravel" , "Writer of music" , "A maker of music" , "Beethoven or Brahms, for instance" .)