Military Stationed in Korea-Indiana County residence

My son is in the US Army stationed in South Korea.  Indiana wants you to give them a county of residence.  The instructions said to pick out of state other state because the military does not hold out local taxes and they should not pay local income tax because they did not live or work in a county.  When the Indiana state tax updated it will not submit unless I pick a county and the instructions have changed.  If I pick a county he will have to pay state taxes