1918 United States Senate election in South Dakota

The 1918 United States Senate election in South Dakota took place on November 5, 1918. Incumbent Republican Senator Thomas Sterling sought re-election in his first popular election. He defeated former Governor Frank M. Byrne in the Republican primary and then faced former State Representative Orville Rinehart, the 1916 Democratic nominee for Governor, in the general election. Sterling defeated Rinehart, along with independent candidate W. T. Rafferty, by a wide margin to win re-election.

Candidates

 * Orville V. Rinehart, former State Representative from Pennington County, 1916 Democratic nominee for Governor
 * James Coffey, Internal Revenue Collector for North and South Dakota
 * John E. Kelley, former U.S. Congressman from South Dakota's at-large congressional district

Candidates

 * Thomas Sterling, incumbent U.S. Senator
 * Frank M. Byrne, former Governor of South Dakota

Candidates

 * John C. Knapp

Results
After winning the primary, Knapp withdrew as a candidate, citing his disagreement with the Socialist Party's anti-war policies.