File an Annual Report File an annual report for a Corporation, Not-for-Profit, or Limited Liability Company online. Corporations must complete Form IL-1120.Do not send a computer printout with line numbers and dollar amounts attached to a blank copy of the return. Curious about the steps needed to form a C Corp in Illinois? The requirements are not overly complicated, but new owners must be thorough in their efforts. To form a corporation, file the original and a copy of the articles of incorporation with the Illinois Secretary of State and pay a filing fee. 1. Choose a business name for the corporation and check for availability.