South Dakota’s two U.S. Senators are Republicans John Thune and Mike Rounds. Thune is the senior senator and currently serves as Senate Majority Leader; Rounds is the junior senator, and his seat is on the ballot in November 2026.
John Thune, Senior Senator
John Thune has represented South Dakota in the Senate since January 3, 2005.1Congress.gov. Senator John Thune In November 2024, Senate Republicans elected him Majority Leader for the 119th Congress, succeeding Mitch McConnell. In that role he controls the Senate’s floor schedule, decides which bills come up for a vote, and speaks for the majority party.2United States Senate. About Parties and Leadership – Majority and Minority Leaders His current term runs through January 3, 2029.3United States Senate. Class III Senators Whose Terms of Service Expire in 2029
Thune sits on three standing committees that matter for South Dakota’s economy: Agriculture, Nutrition, and Forestry; Commerce, Science, and Transportation; and Finance. He also holds ex officio membership on the Select Committee on Intelligence.4Congress.gov. Senator John Thune – Committee Assignments
Mike Rounds, Junior Senator
Mike Rounds took office on January 6, 2015.5GovTrack.us. Sen. Mike Rounds His current term ends January 3, 2027, and he announced his campaign for a third term in January 2026.
Rounds serves on the Appropriations Committee, the Armed Services Committee, the Banking, Housing, and Urban Affairs Committee, the Indian Affairs Committee, and the Select Committee on Intelligence.6Congress.gov. Senator Mike Rounds – Committee Assignments Those seats give him a direct hand in defense spending, tribal policy, and the federal budget, which matters for a state with a significant military presence and several tribal nations.
The 2026 Senate Election in South Dakota
The primary for Rounds’ Class II seat is scheduled for June 2, 2026, with the general election on November 3. A primary runoff, if needed, is set for July 28.7Ballotpedia. United States Senate Election in South Dakota, 2026
Major-party candidates must file nominating petitions with the Secretary of State by 5:00 p.m. CT on March 31, 2026. Independent candidates have until April 28.8South Dakota Secretary of State. 2026 Candidate Calendar There is no filing fee; candidates gather petition signatures instead. The threshold depends on party affiliation:
- Republican: 2,171 signatures
- Democrat: 1,232 signatures
- Libertarian: 741 signatures
- Independent: 3,502 signatures
Each number equals one percent of the party’s vote total in the 2022 gubernatorial race, or one percent of the overall gubernatorial vote for independents.9South Dakota Secretary of State. Number of Signers Required for Candidate Petitions in 2026 A Financial Interest Statement must be filed within 15 days of submitting nominating petitions.
Contacting Senator Thune or Senator Rounds
Both senators keep offices in Washington and staff regional offices across South Dakota. Thune’s in-state offices are in Sioux Falls, Rapid City, and Aberdeen.10John Thune U.S. Senator for South Dakota. Contact Me in South Dakota Rounds runs offices in Sioux Falls, Rapid City, Aberdeen, and Pierre.11U.S. Senator Mike Rounds. Office Locations
Regional-office staff handle constituent casework: helping residents deal with the Social Security Administration, the Department of Veterans Affairs, the IRS, and other federal agencies. If you are stuck waiting on a passport, a veterans’ benefit, or a federal tax issue, calling a senator’s regional office is often the fastest way to get someone to look into it.
Service Academy Nominations
Each senator can nominate South Dakota residents for admission to West Point, the Naval Academy, the Air Force Academy, and the Merchant Marine Academy. Applicants must be unmarried U.S. citizens with no dependents, between 17 and 22 years old as of July 1 of the year they seek admission, and residents of South Dakota. Applications require a high school transcript, ACT or SAT scores, and three letters of recommendation, one of which must come from a school principal or guidance counselor. Thune’s office sets a November 1 deadline for completed packets.12John Thune U.S. Senator for South Dakota. Academy Nominations Rounds’ office runs a similar process on its own timeline, so applicants should check both and apply through each to improve their odds.
If a Seat Becomes Vacant
If a South Dakota Senate seat opens up mid-term, the governor appoints someone on a temporary basis until a special election can be held. There is one exception: if the departing senator’s term was already set to expire at the next regular election, no special election is required. When a vacancy opens within 90 days of a general election, the race to fill it appears on the same ballot as that general election.13South Dakota Legislature. Codified Law 12-11 – Special Congressional Elections