One wearing deerstalker maybe — one in country (5)
I believe the answer is:
haiti
'country' is the definition.
(Haiti is a country)
'one wearing deerstalker maybe one in' is the wordplay.
'one' becomes 'i' (Roman numeral).
'wearing deerstalker maybe' becomes 'hat' (I can't justify this - if you can you should give a lot more credence to this answer).
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'hat'+'i'='hati'
'i' put within 'hati' is 'HAITI'.
Can you help me to learn more?
(Other definitions for haiti that I've seen before include "Country SE of Cuba" , "Western part of island discovered by Columbus in 1492" , "West part of Hispaniola" , "Country in W Indies, capital Port-au-Prince" , "W. Indies republic on Hispaniola" .)