Your tax engine has not been looked at since the last state letter. Three things changed on October 1 and one window closed on October 31. Two of them are settings your engine should already have. The other two are decisions with a dollar amount attached, and they are still open.
The short version: Los Angeles County and Washington, D.C. raised rates on October 1. Pennsylvania moved its local taxes from the seller's location to the customer's address, enforced since October 1 under a law that reaches back to January. Illinois offered to waive penalties and interest for remote sellers who paid old tax by October 31, and that offer has expired. The Pennsylvania history and the Illinois exposure are the two decisions.
Pennsylvania: 2% of every Philadelphia order, and nine months of history
Until this year, Pennsylvania's local sales taxes, 2% in Philadelphia and 1% in Allegheny County, were charged based on where the seller sat. An out-of-state brand collected the state's 6% and nothing local. Act 21 of 2026, signed July 12, flips that. The Department of Revenue's guidance says vendors already required to collect the state tax "are required to collect and remit Philadelphia's 2 percent local sales tax and Allegheny County's 1 percent local sales tax on taxable sales made to customers in those respective counties," and that "the department will not begin enforcing these new rules until October 1, 2026." That date has passed. If your checkout still charges a flat 6% on a Philadelphia delivery, every order since October 1 is 2% short, and the shortfall is the vendor's to remit.
The money question is the history. The law applies to tax years after December 31, 2025. Philadelphia's own notice of September 8 told businesses to "start collecting and remitting local sales taxes right away." Neither page says what happens to the January-through-September tax that nobody collected. As an illustration only, a brand shipping $600,000 a year into Philadelphia owes $12,000 a year of local tax it was not charging, and three quarters of the year ran before enforcement began. Remit it, reserve for it, or document why you will not: decide with your advisor before you file the return that covers October. Marketplace orders are a separate check: confirm the marketplace is collecting local tax on Pennsylvania deliveries.
Illinois: the 9% offer is gone, the 15% risk is not
Illinois has wanted destination-based tax from remote sellers since 2021: the state rate plus the local rate at the delivery address. Plenty of brands crossed the threshold and never registered, or set up the 6.25% state rate and nothing else. From August 1 through October 31 the state offered a deal in Bulletin FY 2026-28: pay a flat 9% on general merchandise for sales from January 1, 2021 through June 30, 2026 through a simplified return, and "related penalties and interest" were waived, with payment plans up to 24 months for anyone who applied by October 31. If you took the payment plan, interest on the unpaid balance started November 1, and a missed installment cancels the deal.
If you did not take it, the alternative in the same bulletin still stands: if Illinois audits and you cannot show where the sales went, "IDOR will assess tax on the gross receipts of such sales to undetermined tax locations at the rate of 15%," and that rate can be applied to periods before 2026. As an illustration only, a brand that did $400,000 a year in Illinois over that period was looking at roughly $200,000 under the amnesty; the same sales at the 15% rate come to roughly $330,000 before penalties and interest. The decision now is whether to register and start collecting at the right rates, and how large a reserve to carry for the years you did not. There is also a balance-sheet point: an uncollected sales tax exposure is a liability a buyer's diligence team will find, and it comes off the price.
Los Angeles and D.C.: half a point and a full point
Since October 1, Los Angeles County has been at 10.25% countywide, up from 9.75%, and dozens of its cities are at 11% or more. Washington, D.C. went from 6% to 7%. If you charge tax at checkout, this was a rate-table update, and California posted the new codes on September 1. If you advertise one tax-inclusive price nationwide, you have been giving up half a point of margin on every Los Angeles order and a full point on every D.C. order for six weeks.
What to ask whoever handles your sales tax
- Is Pennsylvania set to charge local tax by delivery address, and is our marketplace doing the same?
- What do we owe Philadelphia and Allegheny County for January through September, and what is our position on it?
- Are we registered in Illinois, what rate have we been collecting since 2021, and what is the exposure at the 15% rate?
- Are the October 1 California and D.C. rates loaded, and which of our prices are tax-inclusive?
Where your facts change the answer
Whether you owe the Pennsylvania history depends on when you crossed the state's threshold and on what the department publishes about the period before October 1. The Illinois program was for remote retailers; a brand with inventory in an Illinois warehouse was outside it. Marketplace facilitator rules differ by state. None of this replaces a nexus review of your own numbers.
ECOM CPA does not register brands for sales tax or prepare the returns; we refer that work to TaxValet. What we do is reconcile the tax you collect against what you remit as part of the monthly close, and record the Pennsylvania history and the Illinois exposure as liabilities so they sit on the balance sheet before a lender or a buyer finds them. If those two numbers are not in your books yet, that is the monthly accounting work for this month.
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