Is Polymarket legal in Missouri?

Attorney General Catherine L. Hanaway's office addressed the letter, dated September 16, 2026, to "QCX Limited Liability Company ('Polymarket')" through its registered agent in Wilmington, Delaware. It opens: "Polymarket is an online sports wagering platform offering sports wagering to individuals located in the State of Missouri, despite not submitting to regulation by the Missouri Gaming Commission as required by Missouri law" (p.1). The office's release says it sent letters to six prediction markets, Polymarket among them.

The letter is built like the one Kalshi got the same day: a license from the Missouri Gaming Commission, the 10% tax on operators' sports wagering revenue and license fees it says "could be as much as $500,000", and Missouri's minimum age of 21 (pp.1-2). Kalshi in Missouri walks through each of those points and the constitutional amendment behind them.

Two parts are Polymarket's own. On age, the letter targets Polymarket's "US Rulebook", which it says lets anyone at least 18 who has "attained the age of majority in their state and/or country of residence" trade, and says Polymarket "has no authority to allow sports wagering by persons in Missouri under 21" (p.2). And it answers Polymarket's federal argument by name: Missouri "is aware that Polymarket has sought to avoid complying with similar sports gambling laws of other states by claiming that it offers 'event contracts'" governed by the Commodity Exchange Act (p.2). Missouri says it "shares the same view as the majority of federal courts" and cites eight decisions (p.2). Every one of them involves Kalshi or Nadex; none involves Polymarket.

Stop offering sports wagering in Missouri, or get a Missouri Gaming Commission license, pay the state's taxes and fees, and stop offering sports wagering to anyone in Missouri under 21 (p.1). "We ask that you confirm Polymarket's compliance with Missouri law or its cessation of sports wagering activities in the State of Missouri within thirty days of the date of this letter" (p.3). That ran to October 16, 2026. Otherwise, it says, "the State of Missouri will take legal action against Polymarket", while adding that Missouri "remains open to possible legislative reforms in the future" (p.3).

As of October 23, 2026, we found no Missouri lawsuit or order against Polymarket US, no suit by Polymarket US against Missouri, and no attorney general release about Polymarket after the cease-and-desist. Polymarket's reply, if any, is not public.

The letter's demands are about offering sports wagering; it says nothing about accounts, open positions, deposits or withdrawals, and no court order we found in Missouri does. We could not confirm from a primary source whether Polymarket US has changed anything for Missouri users, including its age rule. Polymarket's international site lists the United States as close-only (existing positions can be closed, new ones cannot be opened); the letter is addressed to QCX LLC, the US exchange. Every other state is on Polymarket's legal status page.

Missouri's thirty days ran out on the same day Polymarket US took a different state to court. In Ohio, after the Casino Control Commission gave it fourteen days to stop, QCX LLC sued the attorney general and the Commission in federal court in Columbus on October 16, 2026, arguing preemption and the Commerce Clause (complaint). In other states the fight has gone further:

• New York. The attorney general sued Polymarket US in state court on September 24, 2026; it moved the case to federal court the same day and has its own suit against the attorney general (Polymarket in New York).
• Michigan. Polymarket US sued in federal court in March 2026 and was denied a preliminary injunction on June 17; its appeal is before the Sixth Circuit (Polymarket in Michigan).
• Nevada. A Carson City court granted the state a preliminary injunction against Polymarket US on May 29, 2026 (Polymarket in Nevada).

Missouri's federal courts sit in the Eighth Circuit, where we found no ruling on these contracts. Kalshi's appeal from Iowa, KalshiEX v. Bird, No. 26-2874, is pending there, and Kalshi's side of it is on Kalshi in Missouri.

Missouri calls Polymarket US an unlicensed sports wagering platform; Polymarket US's position is that it is a CFTC-designated exchange whose contracts federal law governs. Either way the letter is about licensing, and the tax it cites is Missouri's levy on an operator's sports wagering revenue, not on a trader's gains. The IRS has not issued guidance on event contracts.

The three routes we see most often among people who file are gambling winnings and losses under section 165(d), standard capital gains on Form 8949, and the Section 1256 60/40 rule on Form 6781. How Realize rebuilds a Polymarket US year under each is in how to file Polymarket taxes.