I am assuming that, after the court date where the Defendant failed to appear, a default judgment was entered in your favor and against the Defendant for the amount you requested from the Court. If this is the case, you must send notice of this judgment to the other driver.
If he fails to respond to it, you will have to use the Courts to enforce the judgment. You can file a Motion to Discover Assets and force the Defendant to return back to Court to inform the Court, under oath, information regarding his assets (jobs, property, investments, etc.). After this, and if the Defendant continues to disregard the Order to pay, then you can/will have to file another motion to garnish his wages. This requires his employer to withhold a certain amount from his paycheck to be turned over to you.
As this is in Illinois, you have another option outside of the Courts. You can contact the Secretary of State and give them notice that there is an outstanding judgment against the driver. Based on this, the Secretary of State will suspend his license until he starts making payments.
Depending on the amount that is owed, he may be considered "judgment proof." If, for instance, someone has a judgment against them for millions of dollars with minimal assets, you can try as hard as you want to collect, but the individual will simply be unable to pay. However, because this is in small claims court, I am under the assumption the damages in this case are minimal (less than $10,000.00).