Capital city, south of Iowa (5)
I believe the answer is:
sofia
'capital city' is the definition.
(I've seen this before)
'south of iowa' is the wordplay.
'south' becomes 's' (abbreviation).
'iowa' becomes 'IA' (abbreviation).
's'+'of'+'ia'='SOFIA'
(Other definitions for sofia that I've seen before include "Bulgarian capital" , "seat of government" , "Bulgarian city" , "capital city" , "European city" .)