| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 12,934 | 23,982 | 37,567 | |
| 2020 | R | 11,141 | 21,669 | 33,445 | |
| 2016 | R | 7,718 | 18,096 | 27,959 | |
| 2012 | R | 8,805 | 16,289 | 25,762 | |
| 2008 | R | 8,761 | 15,744 | 24,984 | |
| 2004 | R | 6,665 | 15,870 | 22,631 | |
| 2000 | R | 5,040 | 11,502 | 17,024 | |
| 1996 | R | 4,989 | 8,290 | 15,003 | |
| 1992 | R | 3,465 | 7,818 | 14,777 | |
| 1988 | R | 3,130 | 8,846 | 12,071 | |
| 1984 | R | 2,579 | 9,336 | 12,001 | |
| 1980 | R | 3,038 | 7,576 | 11,186 | |
| 1976 | R | 4,377 | 7,464 | 12,043 | |
| 1972 | R | 2,447 | 8,389 | 11,054 | |
| 1968 | R | 2,431 | 6,415 | 10,238 | |
| 1964 | R | 4,985 | 5,504 | 10,489 | |
| 1960 | R | 3,116 | 7,838 | 10,954 | |
| 1956 | R | 2,653 | 7,575 | 10,228 | |
| 1952 | R | 2,843 | 7,761 | 10,604 | |
| 1948 | R | 3,008 | 5,688 | 8,713 | |
| 1944 | R | 2,907 | 6,908 | 9,815 | |
| 1940 | R | 3,947 | 7,214 | 11,161 | |
| 1936 | R | 5,157 | 5,673 | 10,950 | |
| 1932 | D | 4,943 | 4,912 | 9,969 | |
| 1928 | R | 2,386 | 5,876 | 8,331 | |
| 1924 | R | 2,571 | 5,256 | 8,378 | |
| 1920 | R | 3,286 | 6,544 | 9,865 | |
| 1916 | R | 2,747 | 3,182 | 6,007 | |
| 1912 | D | 2,362 | 2,051 | 5,807 | |
| 1908 | R | 2,568 | 3,567 | 6,253 | |
| 1904 | R | 1,924 | 3,646 | 5,723 | |
| 1900 | R | 2,484 | 3,561 | 6,151 | |
| 1896 | R | 2,736 | 3,476 | 6,279 | |
| 1892 | R | 2,055 | 3,001 | 5,531 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Union County sits northwest of Columbus and has absorbed significant suburban spillover growth, yet its presidential margins have remained consistently above R+25 since 2000, suggesting new residents skew toward the county's existing political profile.
The Republican margin in Union County reached its widest at fifty-six points in 1984. The margin in 2024 was twenty-nine points, in line with the county's deep historical pattern.
Union County's loyalty is rooted in its place. Median household income of $112,322, a 85% non-Hispanic-white share, and a population of 67,324 together describe a community whose political habits are deeply settled. The county's voting pattern over the last decade is most similar to that of Hamilton County and Greene County.