| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 4,240 | 12,189 | 16,662 | |
| 2020 | R | 4,608 | 12,476 | 17,436 | |
| 2016 | R | 4,425 | 11,695 | 16,999 | |
| 2012 | R | 6,089 | 9,811 | 16,320 | |
| 2008 | R | 7,462 | 9,302 | 17,141 | |
| 2004 | R | 6,713 | 10,160 | 16,948 | |
| 2000 | R | 6,685 | 8,362 | 15,360 | |
| 1996 | D | 7,263 | 5,937 | 14,981 | |
| 1992 | D | 8,665 | 5,497 | 17,597 | |
| 1988 | D | 7,729 | 7,624 | 15,426 | |
| 1984 | R | 7,200 | 9,642 | 16,885 | |
| 1980 | R | 6,761 | 8,972 | 16,340 | |
| 1976 | D | 8,989 | 7,422 | 16,520 | |
| 1972 | R | 6,396 | 9,448 | 15,905 | |
| 1968 | R | 6,476 | 7,367 | 15,467 | |
| 1964 | D | 9,653 | 6,248 | 15,901 | |
| 1960 | R | 7,784 | 9,841 | 17,625 | |
| 1956 | R | 8,090 | 9,637 | 17,727 | |
| 1952 | R | 8,698 | 9,841 | 18,558 | |
| 1948 | D | 8,928 | 7,393 | 16,321 | |
| 1944 | D | 8,496 | 7,916 | 16,551 | |
| 1940 | D | 10,887 | 8,692 | 19,715 | |
| 1936 | D | 10,240 | 7,290 | 17,668 | |
| 1932 | D | 9,495 | 5,333 | 15,005 | |
| 1928 | R | 5,905 | 7,326 | 13,301 | |
| 1924 | D | 6,258 | 5,406 | 12,130 | |
| 1920 | R | 4,772 | 5,711 | 10,660 | |
| 1916 | D | 6,685 | 6,028 | 12,996 | |
| 1912 | D | 3,237 | 1,834 | 6,614 | |
| 1908 | D | 3,377 | 3,210 | 6,787 | |
| 1904 | R | 2,462 | 3,063 | 5,967 | |
| 1900 | D | 3,332 | 2,805 | 6,343 | |
| 1896 | D | 3,588 | 2,603 | 6,307 | |
| 1892 | D | 2,332 | 1,949 | 5,234 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Jefferson County's R+47.7 margin in 2024 reflects the broader partisan shift that has reshaped rural southern Illinois over the past two decades, leaving it among the state's most lopsided counties despite a mid-sized population near 40,000.
The Democratic margin in Jefferson County peaked at twenty-eight points in 1932. By 2000 the county had flipped, voting Republican for the first time in many years. The 2024 margin was forty-eight points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Jefferson County's median household income of $63,118 sits well below state and national norms, and 14% 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 Hamilton County and Moultrie County.