Legal Question in Business Law in Illinois

You don't have to register in every state, but beyond that the answer gets fuzzy. Each state (and country) has its own requirements for what constitutes "doing business" for the purposes of registration. In fact, many states apply different tests to different laws even within their states. For example, many states have adopted rules for collecting sales taxes that are different from the rules for registering as a business entity with the state. The basic test is whether you have enough contact with the state to satisfy the constitutional requirement of "minimum contacts." Starting out, the answer is probably that you have no registration requirements other than Illinois, but you will need to review that answer as your business grows and evolves.