| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 51,168 | 86,271 | 139,355 | |
| 2020 | R | 48,725 | 80,382 | 131,011 | |
| 2016 | R | 34,337 | 66,707 | 105,710 | |
| 2012 | R | 32,473 | 61,107 | 94,728 | |
| 2008 | R | 31,189 | 54,123 | 86,089 | |
| 2004 | R | 17,974 | 42,820 | 61,001 | |
| 2000 | D | 31,876 | 14,890 | 47,161 | |
| 1996 | R | 11,525 | 18,802 | 32,970 | |
| 1992 | R | 10,789 | 16,542 | 31,992 | |
| 1988 | R | 8,820 | 17,015 | 25,896 | |
| 1984 | R | 7,048 | 16,885 | 23,968 | |
| 1980 | D | 10,073 | 9,012 | 19,688 | |
| 1976 | D | 10,578 | 6,184 | 16,840 | |
| 1972 | R | 3,886 | 10,264 | 14,336 | |
| 1968 | R | 3,630 | 5,290 | 13,681 | |
| 1964 | D | 7,208 | 4,229 | 11,437 | |
| 1960 | D | 7,393 | 4,030 | 11,423 | |
| 1956 | D | 6,383 | 3,362 | 9,745 | |
| 1952 | D | 7,416 | 3,790 | 11,206 | |
| 1948 | D | 3,407 | 738 | 5,144 | |
| 1944 | D | 5,729 | 1,114 | 6,843 | |
| 1940 | D | 7,179 | 634 | 7,813 | |
| 1936 | D | 7,480 | 601 | 8,081 | |
| 1932 | D | 6,103 | 710 | 6,870 | |
| 1928 | D | 2,840 | 2,448 | 5,288 | |
| 1924 | D | 2,721 | 672 | 3,425 | |
| 1920 | D | 4,168 | 1,404 | 5,572 | |
| 1916 | D | 2,662 | 702 | 3,368 | |
| 1912 | D | 1,786 | 92 | 2,354 | |
| 1908 | D | 2,029 | 834 | 2,863 | |
| 1904 | D | 1,181 | 379 | 1,580 | |
| 1900 | D | 1,790 | 864 | 2,676 | |
| 1896 | D | 2,747 | 1,009 | 3,779 | |
| 1892 | D | 1,798 | 572 | 3,200 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Union County has absorbed rapid exurban growth from the Charlotte metro yet maintained presidential margins above R+20 for over a decade, making it one of the most reliably right-leaning fast-growth counties in the Southeast.
The unraveling was not abrupt. The Democratic margin in Union County peaked at eighty-five points in 1936; it narrowed steadily over the late twentieth century. The 2004 election delivered the county to the Republican party for the first time in many years, by a margin of forty-one points. By 2024, the margin had settled into deep Republican territory.
The economic and demographic context is severe. Union County's median household income of $102,900 is among the lowest of any county in the United States; 8% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Johnston County and Hughes County.