Here's a link to the actual Illinois law: http://www.ilga.gov/legislation/ilcs/ilcs4.asp?DocName=003500050HArt%2E+3&ActID=577&ChapterID=8&SeqS...
Section 304 (a)(2)(B)(i and ii) state that "Compensation is paid in this state [and taxable by Illinois] if the Individual's service is performed entirely in this state"; or "both within and without this state".
If your service is performed entirely without (outside) Illinois, it is not taxable by Illinois.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
