Illinois lesson 5 of 6
Register with the Illinois Department of Revenue
Filing with the Secretary of State creates the LLC, but it does not register the business for state taxes. That is a separate step with the Illinois Department of Revenue.
Who must register and how
Any LLC conducting business in Illinois or with Illinois customers generally must register with the Illinois Department of Revenue, including businesses that withhold Illinois income tax for employees. Registration is done through Form REG-1, the Illinois Business Registration Application, and can be filed online through MyTax Illinois or on paper.
Which taxes typically apply
Depending on activity, an Illinois LLC may need to collect sales and use tax, withhold Illinois income tax for employees, or register for other industry-specific taxes the Department administers. The registration form asks about each activity so the Department can assign the right accounts.
Registering late does not remove a tax obligation that already existed; it just adds the risk of penalties once the Department catches up with unregistered activity.
Key takeaways
- Secretary of State formation and Department of Revenue tax registration are two separate steps.
- Form REG-1, filed on paper or through MyTax Illinois, covers most state tax registrations.
- Which taxes apply depends on your specific business activities.
Frequently asked questions
Is Illinois Department of Revenue registration the same as getting an EIN?
No. The EIN is a federal number from the IRS. Illinois Department of Revenue registration is a separate state process using Form REG-1 or MyTax Illinois.
Official sources
Or let us file your Illinois LLC for you
Everything above is yours to use for free. If you would rather hand it over, we prepare and file the Articles of Organization (Form LLC-5.5), act as your registered agent, and track your ongoing deadlines.
Last reviewed: September 2026 - reviewed by Gullia Filing Legal & Formation Team