The Illinois DMV site states that he can use his out-of-country license for 90 days. After that he will need to have an Illinois Driver's License. (You will find this under 'New to Illinois" on the left hand side of their website).
Here is a link to the required documentation and what is acceptable for a Driver's License:
http://www.sos.state.il.us/departments/dri...eptable_id.htmlHe will require a SSN. Illinois does accept I-94s as long as it is still valid along with a valid passport. It looks like he will require his birth certificate or passport to prove his age along with some proof of his residency address. For Georgia I used a bank statement addressed to me at my Georgia address.
He should apply for his SSN when he has been here 2 weeks so that his name will be in the Immigration SAVE system. It will take about another 2 weeks or so to arrive. He will need a valid I-94 with more than 2 to 3 weeks of validity left on it. If the I-94 is expired he will have to wait for an EAD for both the SSN and the Driver's License. These are things you want to attend to as soon as you can before the I-94 expires. Good luck.