| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 1,773 | 4,464 | 6,374 | |
| 2020 | R | 1,985 | 4,654 | 6,785 | |
| 2016 | R | 2,014 | 4,058 | 6,493 | |
| 2012 | R | 2,867 | 3,265 | 6,296 | |
| 2008 | D | 3,542 | 3,141 | 6,808 | |
| 2004 | R | 3,215 | 3,907 | 7,183 | |
| 2000 | R | 3,192 | 3,411 | 6,772 | |
| 1996 | D | 3,385 | 2,430 | 6,444 | |
| 1992 | D | 3,969 | 2,473 | 7,702 | |
| 1988 | R | 3,406 | 3,424 | 6,855 | |
| 1984 | R | 3,354 | 4,109 | 7,486 | |
| 1980 | R | 2,680 | 4,644 | 7,693 | |
| 1976 | D | 3,947 | 3,847 | 7,849 | |
| 1972 | R | 2,901 | 4,897 | 7,810 | |
| 1968 | R | 3,365 | 3,899 | 7,853 | |
| 1964 | D | 4,857 | 2,833 | 7,690 | |
| 1960 | R | 3,824 | 4,337 | 8,180 | |
| 1956 | R | 3,199 | 4,677 | 7,889 | |
| 1952 | R | 3,061 | 4,982 | 8,047 | |
| 1948 | R | 3,503 | 3,525 | 7,074 | |
| 1944 | R | 3,282 | 3,959 | 7,262 | |
| 1940 | R | 4,416 | 4,541 | 8,998 | |
| 1936 | D | 5,278 | 3,395 | 8,731 | |
| 1932 | D | 5,681 | 2,551 | 8,300 | |
| 1928 | R | 3,246 | 3,956 | 7,221 | |
| 1924 | R | 2,536 | 3,522 | 6,680 | |
| 1920 | R | 2,595 | 3,842 | 6,579 | |
| 1916 | D | 3,886 | 3,029 | 7,136 | |
| 1912 | D | 2,173 | 948 | 4,121 | |
| 1908 | D | 2,264 | 1,924 | 4,424 | |
| 1904 | D | 1,806 | 1,798 | 3,992 | |
| 1900 | D | 2,508 | 2,027 | 4,636 | |
| 1896 | D | 2,407 | 2,100 | 4,582 | |
| 1892 | D | 2,211 | 1,614 | 4,034 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Mason County's population of roughly 16,000 sits along the Illinois River bottomlands, and its electorate has shifted decisively rightward over successive presidential cycles, posting a 42-point Republican margin in 2024.
The Democratic margin in Mason County peaked at thirty-eight points in 1932. By 2012 the county had flipped, voting Republican for the first time in many years. The 2024 margin was forty-two points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Mason County's median household income of $62,845 sits well below state and national norms, and 15% 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 Scott County and Iron County.