At work or not I'm surprised you can carry concealed in Illinois. I assume you have thoroughly looked in to this?
Yup fixed place of business or private abode is allowed, it's an exemption to UUW laws. (I own the company.)
I also allow my employees to carry at work, if they choose to do so.
EDIT: Also, this has withstood my State's Attorney and local PD's scrutiny. I pulled a firearm on an angry guy who was trying to jump our counter, once. He went down later and filed a report - should have heard the desk sergeant that called me. "I've got this man, down here, he says he was going to jump the counter and attack one of your technicians, and you pulled a gun on him." I laughed, said "yup, that sounds about right."
After the call, I got a visit from the supervisor on duty, he wrote a report, and cleared me of the complaint. Didn't POINT the weapon at the man, just brandished it, which was enough to send him on his merry way.
If I had POINTED the weapon at him, I would have been charged with Assault with a Deadly Weapon, and would have had to go to trial to justify my actions before a judge/jury.
But since I'd only brandished (muzzle never swept a human), I was in the clear. No charges could be filed against me.
I explained to the detective that arrived my philosophy. "If I'd pointed the weapon at him, I would have fired my weapon, and we'd be having an entirely different conversation right now. I don't point a gun at anything I don't intend on shooting."
The detective offered me advice, saying "If you ever DO fire your weapon in self defense, make sure you explain to the responding officer immediately, that you did so in fear of your life. Tell them you were scared, and felt you had no other choice."
State's attorney followed up with me later, expressed the same sentiment.