If we provide alcohol but the guests serve themselves, can we be held liable?

Yes.  You are the "social hosts," particularly if it is at your home, and if you negligently allow a guest to get too drunk, and drive, you could be held liable if they get in an accident.

Alcohol has known potential dangers, and the law won't allow people to turn a blind eye to known potential dangers and ignore the risks without consequences.  Proving negligence of this sort isn't always easy, but you should handle the party expecting to be sued, so you can be prepared if it happens.  At the very least, put the alcohol away at least two hours before you expect people to be driving off.

Great question. Usually those types of laws involve bars and serving those who are obviously drunk (dram shop acts) and serving to minors. 

See the following:

(740 ILCS 58/5)

 Sec. 5. Responsibility of person who supplies alcoholic liquor or illegal drugs to a person under 18 years of age.
    (a) Any person at least 18 years of age who willfully supplies alcoholic liquor or illegal drugs to a person under 18 years of age and causes the impairment of such person shall be liable for death or injuries to persons or property caused by the impairment of such person.

There are laws covering joint tortfeasors for aiding in creating the same problem; however, you will be hardpressed to find this would apply to a party at a private home.   The dram shop act in Illinois (bar drinking for instances) does have caps in what a person can recover but it is a bar to recovery if someone was complicit in the drinking. Therefore, there is no social host liability in your state.  It was the person who drank the alcohol who would be responsible, not the person who provided it.