I believe I was laid off because I testified against an employee(supervisor) who had a compliant filed against him. I did not file the complaint.

The answer will depend partly on the type of complaint that was filed against the supervisor.  If that complaint was based on discrimination, then you can file a charge of retaliation with either the Illinois Department of Human Rights, or the Equal Employment Opportunity Commission. If the complaint that you testified about was not based on discrimination, then you may have a retaliatory discharge action that could be filed in state court. You could still be protected by the law though you did not personally file the complaint.  I strongly recommend that you speak with an employment law attorney to explore the facts in more detail.