Illinois Corporation Taxes

Illinois corporations can face both entity-level income tax and separate annual business taxes, depending on whether the company is treated as a C corporation, an S corporation, or a corporation subject to a separate franchise or margin-tax regime. This guide is rendered from the source-backed tax profile so future updates stay tied to official state tax sources.

At a Glance

Topic	Current treatment
C corporation tax	7% corporate income tax plus 2.5% replacement tax
S corporation tax	1.5% replacement tax
Minimum tax	None listed
Separate business taxes	Yes
Sales tax	Yes — 6.25%

Corporate Income Tax

The current Illinois profile lists a C corporation rate of 7% corporate income tax plus 2.5% replacement tax and an S corporation rate of 1.5% replacement tax.

Illinois corporations and pass-through entities can be subject to replacement tax even when the primary income tax treatment differs.

If your company elected S corporation treatment federally, do not assume the state follows federal law automatically. The state profile is the right place to confirm whether the state recognizes the election and whether it still imposes a separate entity-level tax.

Franchise, Margin, Gross Receipts, and Other Business Taxes

The current profile shows the following business-tax items:

Other (c corp, s corp, partnership): Illinois replacement tax applies at 2.5% for C corporations and 1.5% for S corporations and partnerships.

These taxes can apply in addition to corporate income tax. That distinction matters because a corporation may owe a minimum, franchise, or margin-style tax even in a low-profit year.

Sales Tax for Corporations

Illinois has a base statewide sales tax rate of 6.25%. Local taxes and special district rates can increase the combined Illinois rate.

If the corporation sells taxable goods or taxable services, use Illinois Department of Revenue for registration and rate verification. The current profile points to: https://tax.illinois.gov/businesses/registration.html.

Filing Planning and Entity Choice

The state tax profile is also useful for entity-choice planning. If the S corporation rate, minimum tax, or PTE election rules are materially different from the C corporation rules, that can change whether an S election makes sense. The right comparison is not just federal tax savings; it is the full state stack of income tax, minimum tax, franchise tax, sales tax, and annual compliance cost.

State-Specific Quirks

Replacement tax layer: Illinois entity tax content should always mention replacement tax, not just the headline income tax rate.

Bottom Line

For a Illinois corporation, the main compliance risk is overlooking the extra layer beyond ordinary corporate income tax. Check the minimum tax, the separate business-tax regime, and the state's sales-tax registration rules every time the profile is refreshed.