All LLCs must appoint and maintain a registered agent within Illinois. The company appoints the agent as having the authority to accept the service of process.This system allows you to form or register a Not-for-Profit, Domestic Corporation, or Limited Liability Company or terminate an LLC online. This easytofollow guide has the information you need to create an Illinois LLC online. Ready to start your business? To legally establish your LLC in Chicago, it is mandatory to file the Articles of Organization with the Illinois Secretary of State. The Illinois LLC Act allows for Illinois LLCs to appoint officers such a President, Secretary and Treasurer. That said, all LLCs must register with the Department of Revenue in order to do business in the state. Register your business with the Secretary of State; Get a federal Tax ID; Set up an S Corp with the IRS. If that sounds tough, don't worry.