| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 1,241 | 4,798 | 6,103 | |
| 2020 | R | 1,281 | 5,059 | 6,450 | |
| 2016 | R | 1,142 | 4,649 | 6,089 | |
| 2012 | R | 1,572 | 3,963 | 5,694 | |
| 2008 | R | 1,871 | 3,912 | 5,901 | |
| 2004 | R | 1,813 | 3,997 | 5,865 | |
| 2000 | R | 1,928 | 3,285 | 5,362 | |
| 1996 | R | 2,009 | 2,241 | 4,930 | |
| 1992 | D | 2,299 | 2,124 | 5,391 | |
| 1988 | R | 1,872 | 2,797 | 4,692 | |
| 1984 | R | 1,647 | 3,424 | 5,083 | |
| 1980 | R | 1,586 | 3,201 | 4,888 | |
| 1976 | R | 2,182 | 2,417 | 4,628 | |
| 1972 | R | 1,293 | 2,826 | 4,123 | |
| 1968 | R | 1,143 | 2,406 | 3,975 | |
| 1964 | R | 1,770 | 2,217 | 3,987 | |
| 1960 | R | 1,413 | 2,778 | 4,197 | |
| 1956 | R | 1,549 | 2,973 | 4,524 | |
| 1952 | R | 1,614 | 3,327 | 4,947 | |
| 1948 | R | 1,510 | 2,778 | 4,309 | |
| 1944 | R | 1,522 | 3,298 | 4,833 | |
| 1940 | R | 2,254 | 3,827 | 6,094 | |
| 1936 | R | 2,497 | 3,537 | 6,050 | |
| 1932 | R | 2,387 | 2,424 | 4,861 | |
| 1928 | R | 1,163 | 2,892 | 4,091 | |
| 1924 | R | 1,408 | 2,468 | 4,073 | |
| 1920 | R | 1,137 | 2,972 | 4,191 | |
| 1916 | R | 1,822 | 3,273 | 5,228 | |
| 1912 | R | 952 | 1,025 | 2,923 | |
| 1908 | R | 1,055 | 1,913 | 3,072 | |
| 1904 | R | 980 | 2,164 | 3,321 | |
| 1900 | R | 1,271 | 1,940 | 3,287 | |
| 1896 | R | 1,429 | 2,027 | 3,484 | |
| 1892 | R | 854 | 1,716 | 3,097 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Tucked into the Shawnee Hills at Illinois's southern tip, Johnson County delivered a 58-point Republican presidential margin in 2024, reflecting the deep rural conservatism that defines the state's southernmost counties.
The Democratic margin in Johnson County peaked at three points in 1992. By 1996 the county had flipped, voting Republican for the first time in many years. The 2024 margin was fifty-eight points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Johnson County's median household income of $62,528 sits well below state and national norms, and 18% 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 Todd County and Butler County.