While Illinois is a mandated state, there ARE loopholes... If a company is self-funded, they are not required to provide this coverage. The other loophole, as someone else posted, is that the company has to be incoporated in Illinois.
If you are fortunate enough to work for a company that does not manage to slip through one of these loopholes, be aware that there are qualifications and limitations to most policies. For example, my Illinois BCBS HMO requires (among other things) that we have a doctor document that we have had unprotected sex for one year with no pregnancy resulting. (Duh, I always thought.....like who would want to go through with this if they had other options?)
I have heard that Starbucks and UPS offer infertility coverage, but I do not have any details. When I was considering changing jobs to get coverage, I did a search on the web for companies which provided infertility coverage in the Chicago metro area, and I remember that I did find some listed on some message boards somewhere. However, since it was not necessary for me to pursue that option (long story) I did not do extensive research and I do not remember any of the companies that were listed.
The bottom line, I think, is that each company is different, and there really is no way to find out what you would really need to know before actually being hired.

Such an awful Catch-22.
Good luck!