Military 'broke' lease - do I have to pay back security deposit

[Laura Fazio]

I currently rent a condo in Illinois - 60030 - and had a military family in the home since Jan 2013. I did collect a $1300 deposit upon signing of original lease. Just this year, there was a change in orders and the lease was 'broken' 4 months early. Due to the military reassignment, I do not believe I can go back to them for the 4 months rent. 

My question is...am I legally obligated to pay back the security deposit per Illinois law? I have searched and searched and am unable to locate my answer. I also have questions out to a couple of attorneys and have yet to receive a response. 

I appreciate all the assistance anyone can provide. 

Thank you.