| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 481 | 1,940 | 2,466 | |
| 2020 | R | 565 | 1,966 | 2,580 | |
| 2016 | R | 457 | 1,896 | 2,477 | |
| 2012 | R | 671 | 1,731 | 2,462 | |
| 2008 | R | 923 | 1,668 | 2,650 | |
| 2004 | R | 878 | 1,967 | 2,880 | |
| 2000 | D | 1,758 | 721 | 2,553 | |
| 1996 | R | 939 | 1,461 | 2,789 | |
| 1992 | R | 829 | 1,439 | 2,908 | |
| 1988 | R | 1,094 | 1,940 | 3,060 | |
| 1984 | R | 779 | 2,396 | 3,194 | |
| 1980 | R | 753 | 2,675 | 3,588 | |
| 1976 | R | 1,516 | 2,187 | 3,728 | |
| 1972 | R | 1,287 | 2,416 | 3,711 | |
| 1968 | R | 1,276 | 2,204 | 3,662 | |
| 1964 | D | 1,952 | 1,849 | 3,801 | |
| 1960 | R | 1,468 | 2,406 | 3,874 | |
| 1956 | R | 1,409 | 2,132 | 3,541 | |
| 1952 | R | 1,262 | 2,369 | 3,631 | |
| 1948 | R | 1,513 | 1,607 | 3,155 | |
| 1944 | R | 1,222 | 1,533 | 2,755 | |
| 1940 | R | 1,565 | 1,921 | 3,486 | |
| 1936 | D | 2,212 | 1,420 | 3,666 | |
| 1932 | D | 2,221 | 1,049 | 3,320 | |
| 1928 | R | 1,216 | 1,854 | 3,092 | |
| 1924 | R | 114 | 1,033 | 2,340 | |
| 1920 | R | 478 | 1,411 | 2,298 | |
| 1916 | D | 761 | 590 | 1,383 | |
| 1912 | D | 451 | 0 | 1,121 | |
| 1908 | R | 351 | 825 | 1,214 | |
| 1904 | R | 176 | 654 | 860 | |
| 1900 | R | 282 | 478 | 772 | |
| 1896 | D | 286 | 250 | 541 | |
| 1892 | R | 45 | 187 | 423 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Walworth County, anchored by the small city of Mobridge on the Missouri River, recorded a 59-point Republican presidential margin in 2024 — among the widest gaps in a state already dominated by one-party outcomes at the county level.
The unraveling was not abrupt. The Democratic margin in Walworth County peaked at forty-one points in 2000; it narrowed steadily over the late twentieth century. The 2004 election delivered the county to the Republican party for the first time in many years, by a margin of thirty-eight points. By 2024, the margin had widened further.
The economic and demographic context is severe. Walworth County's median household income of $65,026 is among the lowest of any county in the United States; 15% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Hutchinson County and Tripp County.