I'm not an Illinois attorney, but my research indicates that you do have a sales or use tax obligation -- you have to pay it, as well as adding it to your bills to customers.  My research also suggests that your state's system is one of the most complicated in the nation, and one of the reasons is that there may be local taxes that have to be added on, depending on where you are working.  You need to contact the Illinois Department of Revenue for details.If you have been in business for a while and have not been collecting or paying these taxes, you may well have a serious problem, and if that's the case I would recommend talking to a lawyer in your area, as soon as possible, before doing anything else about this.  One place to look for qualified attorneys is our website, http://attorneypages.com