Girl, our one, in a state (8)
I believe the answer is:
missouri
'a state' is the definition.
(Missouri is an example)
'girl our one' is the wordplay.
'girl' becomes 'miss' (I've seen this before).
'one' becomes 'i' (Roman numeral).
'miss'+'our'+'i'='MISSOURI'
'in' acts as a link.
(Other definitions for missouri that I've seen before include "24th American state to join the Union, 1821" , "River joining the Mississippi south of St Louis" , "Biggest tributary of the Mississippi" , "State of central USA" , "American state's" .)