If you only had one guess at the answer you'd probably get it. 

Did you say Walmart? If you did you get the big prize. Walmart employs the most people in Illinois and 18 other states.  You can peruse all other states at the 24/7 website here. 

A lot has been written about the affect Walmart has on local economies. They don't have the best track record of hiring full time employees and seem to have a take it or leave it approach with most of their workers. But the sheer size of their workforce is certainly daunting.

Other top jobs across the country are medical centers and state universities. Our neighbors to the north fall in the latter of those two with the University of Wisconsin leading the state with over 40,000 employees. It would be interesting to see what the job satisfaction rating is with these monoliths. I'm guessing it's a bit lower than your typical worker.