Polymarket South Dakota: Backed Two Letters, Filed No Suit

Polymarket South Dakota sits in a state that has picked a side without pulling a trigger. South Dakota's attorney general signed onto a 38-state amicus brief backing Massachusetts's lawsuit against Kalshi and a separate 44-state letter telling the CFTC it has no authority over sports event contracts — but as of this writing, no South Dakota cease-and-desist, no state lawsuit, and no injunction has ever named Polymarket directly. The loudest South Dakota voice against prediction markets isn't the AG's office. It's Deadwood.

Legal status in South Dakota

South Dakota's only licensed sports wagering runs through Deadwood: voters approved Constitutional Amendment B in November 2020 (58.5% yes), which let the Legislature authorize in-person sports betting at Deadwood's licensed commercial casinos, regulated by the South Dakota Commission on Gaming. Nine tribal governments — including the Oglala Sioux, Rosebud Sioux, Standing Rock Sioux and Cheyenne River Sioux — can mirror that same offering at reservation casinos under their compacts. There is no statewide mobile or online sportsbook; every legal wager is placed on premises. That could change: the state Senate passed SJR 504 by a 23-10 vote on February 11, 2026, a constitutional amendment that would let the Legislature authorize electronic sports betting through a licensed Deadwood casino with servers required to stay physically in Deadwood, routing 90% of the resulting tax revenue to property-tax relief. If the House concurs, it goes to voters November 3, 2026. None of that framework — Amendment B, Title 42 gaming law, or SJR 504 — was written with event contracts in mind, and none of it currently reaches Polymarket. Where South Dakota has acted is at the multistate level: its attorney general joined roughly 38 states in an April 2026 amicus brief supporting Massachusetts's state-court suit against Kalshi, arguing states retain their traditional authority to regulate gambling, and joined a 44-state coalition letter to the CFTC in July 2026 — led by Ohio Attorney General Andy Wilson — opposing the agency's proposed Rule 40.11 changes as an overreach into ground states have always occupied; only Texas, Florida, Georgia, Missouri and New Hampshire declined to sign that letter, which means South Dakota did. Both actions target the jurisdictional question broadly and neither names Polymarket specifically, distinguishing South Dakota from states like Rhode Island or Nevada that have filed direct actions against Polymarket by name. Separate from the AG, the Deadwood Gaming Association has been the state's most vocal opponent: executive director George Milos has argued publicly that prediction markets let nationwide trading bypass South Dakota's own licensing, age verification, anti-money-laundering rules and self-exclusion programs while paying zero dollars into state gaming tax revenue, and tribal gaming leaders have echoed the complaint. That is industry lobbying and political pressure, not a legal action with binding force. Polymarket US, run by QCX LLC under CFTC designation, currently loads and accepts KYC'd, dollar-funded accounts from a South Dakota address. The international polymarket.com site remains geo-blocked for all US IPs, South Dakota included, under the unrelated 2022 CFTC settlement.

State gambling authority: South Dakota Commission on Gaming licenses Deadwood's in-person sportsbooks and tribal-compact casinos under Amendment B; the Attorney General's office has joined two multistate actions against Kalshi and the CFTC's proposed rule but has not filed a South Dakota case naming Polymarket

Two different South Dakotas are talking about Polymarket right now, and they aren't saying the same thing in the same forum. The attorney general has signed her name to two multistate documents arguing prediction markets overstep state gambling authority. Deadwood's casino industry has gone further, in public, in its own words. Neither has produced a South Dakota order against Polymarket.

Is Polymarket Legal in South Dakota? Depends What Counts as Action

South Dakota's only licensed wagering runs through Deadwood, under Constitutional Amendment B — voters approved it in November 2020, 58.5% yes, and it authorized in-person sports betting at licensed commercial casinos there, plus mirrored offerings at nine tribal-compact casinos statewide. Every legal bet is placed on premises; there is no mobile or online sportsbook today. That statute was never built to reach an event-contract exchange, and nothing in South Dakota's general gambling law has been tested against one in court.

What South Dakota has actually signed: an April 2026 amicus brief (roughly 38 states) backing Massachusetts's lawsuit against Kalshi, and a July 2026 letter (44 states, led by Ohio) telling the CFTC it lacks authority over sports event contracts. Both are coalition positions on the broader legal fight. Neither is a South Dakota case with Polymarket's name on it.

Deadwood Made the Louder Argument

George Milos, executive director of the Deadwood Gaming Association, has said publicly that prediction markets let nationwide trading happen on sporting outcomes South Dakota voters never approved in that format — while sidestepping the licensing, age verification, anti-money-laundering controls and self-exclusion resources Deadwood casinos are required to run, and without contributing a cent to the gaming tax revenue that supports the town's preservation and local services. Tribal gaming leaders have raised a similar complaint. It reads as the state's clearest and most specific objection to the product — and it's industry lobbying aimed at lawmakers, not a court filing.

South Dakota's 2026 timeline so far:

February 11, 2026 — State Senate passes SJR 504, 23-10, teeing up a statewide electronic-betting vote
April 2026 — SD attorney general joins ~38-state amicus brief backing Massachusetts v. Kalshi
2026 — Deadwood Gaming Association and tribal gaming leaders publicly oppose prediction markets
July 2026 — SD attorney general joins 44-state letter opposing CFTC Rule 40.11 changes
November 3, 2026 — SJR 504 goes to voters, if the House concurs

SJR 504 Is About Deadwood, Not Prediction Markets

The ballot measure moving through Pierre would let the Legislature authorize electronic sports betting through a licensed Deadwood casino, with servers required to stay physically in South Dakota and 90% of tax proceeds earmarked for property-tax relief statewide. It's aimed at giving South Dakota its own regulated mobile sportsbook — the kind of product DraftKings or a Deadwood operator would run under a state license. It says nothing about event contracts and wouldn't, on its own, change where Polymarket stands if voters approve it in November.

Is Polymarket Legit and Safe in South Dakota?

Legit: unchanged by any of this. Polymarket US runs under the same CFTC designation, KYC and dollar settlement in South Dakota as everywhere else, and none of the state's objections — the AG's filings, Deadwood's lobbying — allege a bad payout. Safe: an account opens today with nothing blocking it, but South Dakota's attorney general has now taken a public position against the industry's legal theory twice in one year, and the state's own casino lobby wants lawmakers to act. That's a more charged environment than the many states where government has said nothing at all, even without a South Dakota order to point to yet. Deadwood's licensed consumer protections — Commission oversight, self-exclusion, in-person checks — don't reach Polymarket either way.

Watch whether South Dakota follows Rhode Island or Nevada into a direct action, and watch what happens to SJR 504 in November. Until either resolves, an event contract can still lose the full stake no matter which way the jurisdiction fight breaks. This is not a way to make money. 21+ only; the South Dakota Problem Gambling helpline, 1-888-781-4357, is free and confidential.

Polymarket South Dakota — Frequently Asked Questions

Is Polymarket legal in South Dakota?

Untested, not settled. South Dakota's licensed gambling framework covers only Deadwood's in-person casinos and tribal-compact venues under Amendment B — nothing in that law licenses or bans a CFTC-designated exchange. The state has taken multistate positions against Kalshi and against the CFTC's proposed rule, but no South Dakota cease-and-desist, lawsuit, or injunction has ever named Polymarket.

Did South Dakota actually take action against Kalshi or Polymarket?

The attorney general signed two coalition documents: an April 2026 amicus brief backing Massachusetts's lawsuit against Kalshi, and a July 2026 letter from 44 state attorneys general arguing the CFTC lacks authority to regulate sports event contracts. Both target the industry's legal theory broadly rather than filing a South Dakota case against either company by name, so neither is enforcement in the sense a cease-and-desist or lawsuit would be.

Why is Deadwood fighting prediction markets if the state hasn't sued anyone?

Money and control, by the industry's own account. Deadwood Gaming Association executive director George Milos has said publicly that platforms like Kalshi and Polymarket let people trade on sporting outcomes without South Dakota's licensing, age checks, anti-money-laundering controls or self-exclusion programs, and without sending a dollar to the state's gaming tax base that funds Deadwood's historic preservation and local services. Tribal gaming leaders have raised the same complaint. That is advocacy aimed at Pierre and Congress, not a court filing.

Is Polymarket legit in South Dakota?

As a company, that doesn't change state to state: Polymarket US operates under the same CFTC designation, KYC process and dollar settlement in South Dakota as anywhere else. South Dakota's objections — voiced through the AG's multistate filings and Deadwood's lobbying — are about licensing authority and lost tax revenue, not about whether Polymarket honors a winning contract.

Is Polymarket safe to use from South Dakota right now?

Mechanically, yes — an account opens today and nothing has shut it off. But South Dakota's attorney general has publicly aligned against the industry's legal theory twice this year, and Deadwood's casino lobby wants the Legislature to act. That is a more hostile political environment than the many states where nobody in government has said a word, even though it hasn't produced a South Dakota order yet. The consumer protections built into Deadwood's licensed sportsbooks — Commission oversight, self-exclusion, in-person age checks — don't extend to Polymarket either way.

What is SJR 504 and does it have anything to do with Polymarket?

SJR 504 is a constitutional amendment the South Dakota Senate passed 23-10 on February 11, 2026, that would let the Legislature authorize electronic sports betting through a licensed Deadwood casino, with servers required to stay in Deadwood and 90% of tax revenue earmarked for property-tax relief. If the House agrees, it goes to voters November 3, 2026. It is about expanding South Dakota's own licensed, in-state sportsbook model — it does not mention event contracts and would not by itself change Polymarket's status.

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