File an annual report for a Corporation, Not-for-Profit, or Limited Liability Company online. Incorporate a business or terminate an LLC.Learn how to start an S Corp in Illinois, file an LLC, and set up your business. Get step-by-step guidance on starting your business today. To file an S Corporation, first choose a business name and register it. Submit the form to apply for S corporation status. To form an S corporation, designate "S" status with IRS via Form 2553 within 2 months and 15 days of filing your articles of incorporation with Illinois.