| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 20,051 | 35,009 | 56,580 | |
| 2020 | R | 20,606 | 35,063 | 57,518 | |
| 2016 | R | 14,074 | 29,804 | 47,743 | |
| 2012 | R | 15,125 | 28,232 | 44,464 | |
| 2008 | R | 17,802 | 27,603 | 46,280 | |
| 2004 | R | 14,213 | 29,976 | 44,968 | |
| 2000 | D | 1,237 | 297 | 1,614 | |
| 1996 | R | 460 | 983 | 1,692 | |
| 1992 | R | 566 | 872 | 1,991 | |
| 1988 | R | 12,068 | 19,510 | 31,757 | |
| 1984 | R | 8,224 | 21,947 | 30,389 | |
| 1980 | R | 7,121 | 18,991 | 28,204 | |
| 1976 | R | 10,058 | 13,352 | 23,699 | |
| 1972 | R | 8,592 | 13,654 | 22,326 | |
| 1968 | R | 7,303 | 9,671 | 18,148 | |
| 1964 | D | 9,881 | 8,926 | 18,807 | |
| 1960 | R | 7,478 | 11,364 | 18,842 | |
| 1956 | R | 5,332 | 10,955 | 16,287 | |
| 1952 | R | 4,470 | 11,029 | 15,499 | |
| 1948 | R | 4,929 | 6,392 | 11,413 | |
| 1944 | R | 3,517 | 5,246 | 8,763 | |
| 1940 | R | 4,878 | 6,603 | 11,481 | |
| 1936 | D | 5,557 | 4,442 | 10,428 | |
| 1932 | D | 5,178 | 3,638 | 8,875 | |
| 1928 | R | 2,266 | 4,645 | 6,936 | |
| 1924 | R | 854 | 3,201 | 5,035 | |
| 1920 | R | 1,205 | 2,568 | 3,998 | |
| 1916 | R | 1,108 | 1,339 | 2,593 | |
| 1912 | D | 1,135 | 0 | 2,357 | |
| 1908 | R | 1,160 | 1,702 | 2,966 | |
| 1904 | R | 392 | 1,126 | 1,632 | |
| 1900 | R | 784 | 898 | 1,697 | |
| 1896 | D | 1,038 | 739 | 1,785 | |
| 1892 | R | 147 | 959 | 1,893 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Home to Rapid City and the gateway to the Black Hills, Pennington County combines a mid-size urban core with expansive rural terrain. Its R+26 presidential margin in 2024 reflects a consistent pattern of Republican dominance across both areas.
The unraveling was not abrupt. The Democratic margin in Pennington County peaked at fifty-eight 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-five points. By 2024, the margin had settled into deep Republican territory.
The economic and demographic context is severe. Pennington County's median household income of $74,517 is among the lowest of any county in the United States; 11% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Transylvania County and Hughes County.