| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 2,285 | 5,837 | 8,226 | |
| 2020 | R | 2,579 | 6,161 | 8,904 | |
| 2016 | R | 2,402 | 5,790 | 8,616 | |
| 2012 | R | 3,137 | 4,957 | 8,318 | |
| 2008 | R | 3,918 | 5,003 | 9,116 | |
| 2004 | R | 3,735 | 5,333 | 9,119 | |
| 2000 | R | 3,982 | 4,397 | 8,660 | |
| 1996 | D | 4,252 | 3,147 | 8,282 | |
| 1992 | D | 4,681 | 3,003 | 9,083 | |
| 1988 | R | 4,197 | 4,244 | 8,479 | |
| 1984 | R | 3,815 | 4,721 | 8,564 | |
| 1980 | R | 3,781 | 4,289 | 8,441 | |
| 1976 | D | 5,003 | 3,531 | 8,578 | |
| 1972 | R | 3,428 | 5,034 | 8,480 | |
| 1968 | R | 3,603 | 3,889 | 8,372 | |
| 1964 | D | 5,208 | 3,142 | 8,350 | |
| 1960 | R | 4,321 | 4,432 | 8,763 | |
| 1956 | D | 4,359 | 4,204 | 8,569 | |
| 1952 | R | 4,296 | 4,658 | 8,963 | |
| 1948 | D | 4,479 | 3,864 | 8,398 | |
| 1944 | D | 4,367 | 4,114 | 8,527 | |
| 1940 | D | 5,804 | 4,915 | 10,800 | |
| 1936 | D | 6,260 | 4,165 | 10,461 | |
| 1932 | D | 6,157 | 2,859 | 9,085 | |
| 1928 | D | 4,149 | 3,352 | 7,530 | |
| 1924 | D | 3,783 | 2,579 | 6,586 | |
| 1920 | D | 3,660 | 3,119 | 6,847 | |
| 1916 | D | 5,171 | 3,135 | 8,440 | |
| 1912 | D | 2,648 | 1,194 | 4,387 | |
| 1908 | D | 2,690 | 1,695 | 4,529 | |
| 1904 | D | 1,967 | 1,537 | 3,887 | |
| 1900 | D | 2,900 | 1,695 | 4,645 | |
| 1896 | D | 2,998 | 1,842 | 4,892 | |
| 1892 | D | 2,663 | 1,427 | 4,202 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Union County sits in Illinois's rugged southern tip, where the Shawnee National Forest dominates the landscape and a dwindling rural population has shifted presidential margins decisively rightward over the past two decades, reaching R+43.2 in 2024.
The Democratic margin in Union County peaked at thirty-six points in 1932. By 2000 the county had flipped, voting Republican for the first time in many years. The 2024 margin was forty-three points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Union County's median household income of $55,728 sits well below state and national norms, and 20% of residents live below the federal poverty line. The shift here is part of a broader realignment of working-class places across the country. The county's voting pattern over the last decade is most similar to that of Hardin County and Henry County.