How often do I file sales tax returns in Illinois?

Illinois assigns filing frequency based on your expected tax liability: monthly for high-volume sellers, quarterly for mid-volume, annually for low-volume. The DOR may reassign as your activity changes.

What if I had zero sales in Illinois for a period?

You still file a zero return. Missing filings trigger penalties regardless of tax owed. Most tax services file zero returns automatically.

When are Illinois sales tax returns due?

Typically the 20th of the month following the filing period (with variations). Late filing and late payment each carry their own penalty structure — file early to avoid either.

Illinois Sales Tax Filing Guide — 2026

Updated 2026-05-22

If your Filing business sells $100,000 into Illinois in a calendar year, you have economic nexus and must register, collect, and remit Illinois sales tax.

Filing frequency in Illinois

Most states assign a filing cadence when you register, based on your expected tax liability: monthly for high-volume sellers ($50K+ tax liability/year), quarterly for mid-volume, and annually for low-volume. Illinois may reassign your frequency if your liability changes materially.

Zero returns still matter

Even if you had zero taxable sales in Illinois during a period, you must file a zero return. Missing filings trigger penalties regardless of tax owed. Most automated tax services will file zero returns for you by default.

Due dates

Illinois's filing due dates are typically the 20th of the month following the period end (with variations). Late filing penalties are usually 5%/month up to 25%; late payment adds interest. Register for the state's auto-pay or use a service that remits on your behalf to avoid late fees.

Filing mistakes that cost Illinois sellers

Skipping a zero return in a slow month — most penalty exposure comes from missed filings, not unpaid tax.
Waiting until due date to file; Illinois's portal can time out on volume days. File at least 48 hours early.
Not keeping exemption certificates on file — if you're audited and can't produce a valid certificate for a tax-exempt sale, that sale becomes taxable and you owe the uncollected tax.

Illinois nexus note

Illinois sales tax nexus and economic nexus threshold: beginning January 1, 2026, a remote retailer is subject to Illinois state and local Retailers' Occupation Tax when it has $100,000 or more in cumulative gross receipts from sales of tangible personal property to Illinois purchasers during the lookback period. The prior 200-transaction threshold applied from 2021 through 2025 but no longer applies for 2026 and later periods. Remote retailers and marketplace facilitators determine the threshold quarterly for the preceding 12-month period, and destination-based local ROT generally applies when the sale is sourced outside Illinois.

What to do next

Read the full Illinois overview for thresholds, filing frequency, marketplace facilitator rules, and registration links. Use the nexus calculator to check whether you have crossed the threshold. For background on the post-Wayfair economic nexus framework, see the pillar guide.

Frequently asked questions

How often do I file sales tax returns in Illinois?: Illinois assigns filing frequency based on your expected tax liability: monthly for high-volume sellers, quarterly for mid-volume, annually for low-volume. The DOR may reassign as your activity changes.
What if I had zero sales in Illinois for a period?: You still file a zero return. Missing filings trigger penalties regardless of tax owed. Most tax services file zero returns automatically.
When are Illinois sales tax returns due?: Typically the 20th of the month following the filing period (with variations). Late filing and late payment each carry their own penalty structure — file early to avoid either.

Sources

date_retrieved: 2026-05-22