| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 8,278 | 12,347 | 20,995 | |
| 2020 | R | 9,055 | 12,521 | 22,111 | |
| 2016 | R | 7,768 | 11,083 | 20,343 | |
| 2012 | R | 10,165 | 10,512 | 21,128 | |
| 2008 | D | 11,349 | 9,909 | 21,605 | |
| 2004 | R | 8,913 | 12,212 | 21,320 | |
| 2000 | R | 8,062 | 10,715 | 19,378 | |
| 1996 | R | 7,145 | 8,871 | 18,125 | |
| 1992 | R | 7,899 | 9,005 | 21,656 | |
| 1988 | R | 7,460 | 11,342 | 18,945 | |
| 1984 | R | 6,723 | 14,237 | 21,131 | |
| 1980 | R | 6,195 | 10,779 | 20,388 | |
| 1976 | R | 7,192 | 11,678 | 19,137 | |
| 1972 | R | 6,404 | 13,584 | 20,019 | |
| 1968 | R | 7,040 | 11,821 | 19,928 | |
| 1964 | D | 10,854 | 9,252 | 20,106 | |
| 1960 | R | 8,055 | 13,872 | 21,995 | |
| 1956 | R | 6,349 | 14,245 | 20,614 | |
| 1952 | R | 6,605 | 14,446 | 21,086 | |
| 1948 | R | 7,409 | 10,564 | 18,122 | |
| 1944 | R | 7,755 | 11,948 | 19,821 | |
| 1940 | R | 8,911 | 14,040 | 23,045 | |
| 1936 | D | 10,567 | 9,943 | 21,342 | |
| 1932 | D | 10,728 | 8,963 | 20,198 | |
| 1928 | R | 5,579 | 11,992 | 17,643 | |
| 1924 | R | 2,452 | 8,638 | 16,216 | |
| 1920 | R | 2,772 | 9,570 | 12,821 | |
| 1916 | R | 5,463 | 8,620 | 14,744 | |
| 1912 | D | 3,850 | 1,367 | 9,060 | |
| 1908 | R | 4,076 | 4,605 | 9,041 | |
| 1904 | R | 3,275 | 4,876 | 8,611 | |
| 1900 | R | 3,983 | 4,677 | 8,910 | |
| 1896 | R | 3,776 | 4,728 | 8,729 | |
| 1892 | D | 3,717 | 3,574 | 7,643 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Stephenson County sits in Illinois's northwestern corner, anchored by Freeport, and has voted Republican in every presidential race since 2000 by double-digit margins, reflecting broader rural consolidation across the Driftless-adjacent Midwest.
The county's recent history is a story of close margins. The Democratic margin reached twenty-seven points in 1912; the Republican margin reached fifty-three points in 1920. Most other elections have been decided by single-digit points.
Stephenson County's demographics — a population of 43,768, a 80% non-Hispanic-white share, a median household income of $64,043 — situate the county close to national averages on several dimensions. The county's voting pattern over the last decade is most similar to that of Boone County and Halifax County.