| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 971 | 5,224 | 6,231 | |
| 2020 | R | 1,053 | 5,133 | 6,245 | |
| 2016 | R | 1,014 | 4,568 | 5,694 | |
| 2012 | R | 1,339 | 3,980 | 5,393 | |
| 2008 | R | 1,300 | 3,940 | 5,293 | |
| 2004 | R | 1,251 | 3,396 | 4,675 | |
| 2000 | R | 1,407 | 2,332 | 3,826 | |
| 1996 | R | 1,388 | 1,636 | 3,462 | |
| 1992 | R | 1,248 | 1,546 | 3,571 | |
| 1988 | R | 691 | 1,644 | 2,349 | |
| 1984 | R | 761 | 1,804 | 2,567 | |
| 1980 | D | 1,237 | 1,123 | 2,423 | |
| 1976 | D | 1,480 | 544 | 2,040 | |
| 1972 | R | 253 | 1,314 | 1,567 | |
| 1968 | D | 290 | 179 | 1,661 | |
| 1964 | D | 740 | 710 | 1,450 | |
| 1960 | D | 941 | 311 | 1,252 | |
| 1956 | D | 958 | 218 | 1,176 | |
| 1952 | D | 968 | 268 | 1,236 | |
| 1948 | D | 594 | 55 | 874 | |
| 1944 | D | 905 | 102 | 1,007 | |
| 1940 | D | 1,024 | 95 | 1,119 | |
| 1936 | D | 1,089 | 89 | 1,178 | |
| 1932 | D | 897 | 60 | 957 | |
| 1928 | D | 503 | 177 | 689 | |
| 1924 | D | 322 | 16 | 348 | |
| 1920 | — | — | — | — | |
| 1916 | — | — | — | — | |
| 1912 | — | — | — | — | |
| 1908 | — | — | — | — | |
| 1904 | — | — | — | — | |
| 1900 | — | — | — | — | |
| 1896 | — | — | — | — | |
| 1892 | — | — | — | — | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Union County's 2024 presidential margin of R+68.3 ranks among the most lopsided in the state, driven by a rural, majority-white population of roughly 13,000 that includes a substantial share of inmates at the Union Correctional Institution.
The unraveling was not abrupt. The Democratic margin in Union County peaked at eighty-eight points in 1924; it narrowed steadily over the late twentieth century. The 1984 election delivered the county to the Republican party for the first time in many years, by a margin of forty-one points. By 2024, the margin had widened further.
The economic and demographic context is severe. Union County's median household income of $64,146 is among the lowest of any county in the United States; 20% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Columbia County and Clay County.