How does Illinois tax a Limited Liability Corporation (LLC)?
If you are an LLC, the tax return you file with Illinois depends on how you have elected to be treated with the IRS.
If the LLC is treated as a sole proprietorship for federal tax income tax purposes and its income is reported on its owner's U.S. Form 1040, U.S. Individual Income Tax Return, for Illinois purposes the LLC's income will be reported on its owner's Form IL-1040, Illinois Individual Income Tax Return.
If the LLC is a corporation for federal income tax purposes, and files a U.S. Form 1120, U.S. Corporation Income Tax Return, for Illinois purposes the LLC will file Form IL-1120, Corporation Income and Replacement Tax Return.