1984 United States presidential election in South Dakota

The 1984 United States presidential election in South Dakota took place on November 6, 1984. All 50 states and the District of Columbia, were part of the 1984 United States presidential election. Voters chose three electors to the Electoral College, which selected the president and vice president of the United States.

South Dakota was won by incumbent United States President Ronald Reagan of California, who was running against former Vice President Walter Mondale of Minnesota. Reagan ran for a second time with incumbent Vice President and former C.I.A. Director George H. W. Bush of Texas, and Mondale ran with Representative Geraldine Ferraro of New York, the first major female candidate for the vice presidency.

The presidential election of 1984 was a very partisan election for South Dakota, with over 99.5% of the electorate voting for either the Democratic or Republican parties, and only four candidates appearing on the ballot. All but two counties in South Dakota voted in majority for the Republican candidate. This included the typically more Democratic East River counties such as Brown, and Minnehaha (Sioux Falls). Reagan did the best in Haakon County, and Mondale did the best in nearby Shannon County, which gave Mondale his third-best percentage nationwide behind the District of Columbia and Alabama’s Macon County.

South Dakota weighed in for this election as about eight points more Republican than the national average. , this is the last election in which Dewey County, Buffalo County, and Clay County voted for a Republican presidential candidate.

Reagan carried South Dakota by 26.5%, the strongest performance of any presidential nominee in the state since 1952. After nearly voting for Carter in 1976, the state trended much more heavily Republican in both of Reagan's elections; it had been one of only nine to give Reagan over 60% of the vote in the three-way election of 1980. South Dakota became much more competitive in the drought-influenced 1988 election, but would go on to re-establish itself as a reliably red state in the 21st century. Even so, as of 2020, Reagan's 63.00% vote share in South Dakota has remained unmatched by any subsequent nominee.