Per-state pillar
Sales tax in Illinois
Illinois sales tax for small business is administered by the Illinois Department of Revenue (IDOR) on a 6.25% state base layered with home-rule city + county + regional transportation authority + special-purpose-district add-ons — pushing Chicago-ship-to combined to roughly 11.50% (city + Cook County + RTA) while most non-Cook shipments cluster 7.25%–9.00%. This pillar walks through the IDOR cadence, the $100K + 200-transactions two-prong economic-nexus threshold, the Level 1 marketplace-facilitator rule that has applied since 2020, the STLDR-1 / MyTax Illinois registration path, the Form ST-587 exemption-certificate series, and the common operator pitfalls (ST-1 vs. ST-2, home-rule rotation, the marketplace carve-out) — so a small-but-growing Illinois sales-tax footprint can stop hand-rolling the cadence through MyTax Illinois, STLDR-1, and the ST-587 exemption-certificate series.
What you’ll find in this guide
- Monthly ST-1 on the 20th of the month following the period for new and high-liability accounts via Form ST-1 (Sales and Use Tax Return), with the IDOR reclassifying low-liability accounts to quarterly / annual once prior-12-month liability drops below the IDOR thresholds, the always-file-a-no-activity-month ST-1 rule once the seller is registered, the companion Form ST-2 (Use Tax Return) for stored or consumed items where the seller did not collect at the point of sale (details on the IDOR Sales and Use Tax page), and overlapping cadence with the monthly-on-the-20th rhythm in Pennsylvania, Georgia, North Carolina, and Florida for a multi-state operator.
- Illinois's 6.25% state base administered by the IDOR (per the ST-1 instructions (Publication 130)), plus a home-rule city + county + regional-transportation-authority + special-purpose-district add-on — pushing Chicago-ship-to combined to roughly 11.50% (city + Cook County + RTA), other Cook County-ship-to ZIPs roughly 10.25%–10.50%, suburban Cook collar counties 7.75%–9.00%, and most downstate Illinois shipments 7.25%–8.25%.
- The IDOR's Wayfair-aligned but Illinois-set Level 1 two-prong threshold: more than $100,000 in gross receipts AND 200 or more separate transactions from Illinois-bound sales in the prior twelve-month period — both prongs required, no transaction-count-only or dollar-only alternative — so a single high-ticket sale will not trip the threshold on its own and a high transaction count under the dollar trigger likewise does not register the seller. Once crossed, registration runs through the MyTax Illinois portal via Form STLDR-1.
- STLDR-1 / MyTax Illinois registration path, the Level 1 marketplace-facilitator carve-out that has applied since 2020 (only the collection-and-remit obligation on facilitated sales is carved out — the seller still registers STLDR-1 and collects on every direct own-channel sale shipped into Illinois), and the Form ST-587 exemption-certificate series on manufacturing-machinery and qualifying production-related tangible personal property plus intermittent-isolated-sale exempt sales.
- STLDR-1 registration through the MyTax Illinois portal before the close of the month after crossing the Level 1 economic-nexus threshold, the IDOR Certificate of Registration that anchors the always-file-a-no-activity-month ST-1 obligation, the Form ST-587 marketplace-facilitator certificate kept on file to document the carve-out from collection-and-remit on facilitated sales, and the standard Illinois exempt-category list (unprepared groceries, prescription and non-prescription drugs dispensed under a prescription, medical equipment and prosthetics, manufacturing machinery, textbooks sold by a school, occasional isolated sales) where each exempt claim still expects the appropriate Form ST-587 certificate at the point of sale.
Pegged to the IDOR's monthly-on-the-20th ST-1 remittance calendar
Pegged to the IDOR's monthly-on-the-20th ST-1 remittance calendar
Stillpost estimates your Illinois sales-and-use-tax liability off your daily sales and lines it up with the IDOR's monthly 20th-of-the-month remittance calendar — so the estimate lands on the day the IDOR expects the return, not 5 days early or 5 days late. The IDOR may reclassify a monthly account down to quarterly / annual once the prior-12-month liability drops below the IDOR thresholds; Stillpost keeps the same per-period view either way, so the dashboard reads the same for a monthly-on-the-20th permit and a quarterly-downshifting permit. The always-file-a-no-activity-month ST-1 rule the IDOR enforces on every registered seller regardless of activity is reflected in the same per-period view, so even a zero-sales account still files the monthly no-activity ST-1 to keep the Certificate of Registration in good standing. The companion Form ST-2 (Use Tax Return) for stored or consumed items where the seller did not collect at the point of sale is filed on its own cadence with its own penalty window.
On top of the cadence-pegged estimate, you also get the IDOR's Wayfair-aligned but Illinois-set Level 1 $100,000 + 200-transaction two-prong economic-nexus tracker (both prongs required — no transaction-count-only or dollar-only alternative — so a single high-ticket sale will not trip the threshold on its own and a high transaction count under the dollar trigger likewise does not register the seller), with STLDR-1 registration through the MyTax Illinois portal starting on the first of the month after the threshold crosses. The Level 1 marketplace-facilitator carve-out that has applied since 2020 only relieves the collection-and-remit obligation on facilitated sales, so a remote seller who runs both a marketplace channel and a direct own-channel still registers STLDR-1, collects on every direct own-channel sale shipped into Illinois, and keeps a Form ST-587 marketplace-facilitator certificate on file to document the carve-out for the marketplace portion.
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No sales call, no onboarding deck — just a short note when the next feature ships.
Other pillars and verticals
Jump from Illinois into a sibling state pillar or into the vertical surface that fits the inside of your business — every link below renders against the same control plane the Illinois pillar ships, so the rate-overlay / cadence / nexus / marketplace framing reads the same across the cluster.
Sister state pillars