| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 48,116 | 74,878 | 124,678 | |
| 2020 | R | 41,257 | 68,353 | 111,357 | |
| 2016 | R | 28,362 | 54,372 | 85,909 | |
| 2012 | R | 27,290 | 48,427 | 76,691 | |
| 2008 | R | 26,795 | 43,622 | 71,017 | |
| 2004 | R | 17,266 | 36,903 | 54,357 | |
| 2000 | D | 27,212 | 13,704 | 41,155 | |
| 1996 | R | 11,175 | 18,704 | 32,119 | |
| 1992 | R | 11,284 | 15,418 | 31,679 | |
| 1988 | R | 8,717 | 15,563 | 24,329 | |
| 1984 | R | 7,833 | 16,210 | 24,080 | |
| 1980 | R | 9,601 | 10,444 | 20,376 | |
| 1976 | D | 10,301 | 8,511 | 18,879 | |
| 1972 | R | 3,488 | 14,272 | 18,011 | |
| 1968 | R | 4,492 | 6,764 | 20,468 | |
| 1964 | D | 10,326 | 7,523 | 17,849 | |
| 1960 | D | 9,914 | 6,660 | 16,574 | |
| 1956 | D | 9,852 | 4,893 | 14,745 | |
| 1952 | D | 9,997 | 5,429 | 15,426 | |
| 1948 | D | 9,188 | 3,211 | 12,997 | |
| 1944 | D | 8,282 | 4,423 | 12,705 | |
| 1940 | D | 9,976 | 4,192 | 14,168 | |
| 1936 | D | 11,253 | 4,339 | 15,592 | |
| 1932 | D | 9,574 | 3,887 | 13,511 | |
| 1928 | R | 5,041 | 7,696 | 12,737 | |
| 1924 | R | 4,656 | 4,910 | 9,589 | |
| 1920 | D | 6,030 | 5,588 | 11,618 | |
| 1916 | D | 3,468 | 2,857 | 6,325 | |
| 1912 | D | 2,757 | 1,335 | 5,175 | |
| 1908 | R | 2,593 | 2,827 | 5,420 | |
| 1904 | D | 2,572 | 1,553 | 4,125 | |
| 1900 | D | 3,154 | 1,997 | 5,168 | |
| 1896 | D | 3,343 | 1,824 | 5,169 | |
| 1892 | D | 3,135 | 1,036 | 4,791 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Johnston County has absorbed significant population spillover from the Raleigh metro while maintaining a consistent Republican margin, landing at R+21.5 in 2024 despite demographic churn typical of rapidly expanding commuter counties.
The unraveling was not abrupt. The Democratic margin in Johnston County peaked at forty-six points in 1948; 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 thirty-six points. By 2024, the margin had settled into deep Republican territory.
The economic and demographic context is severe. Johnston County's median household income of $83,384 is among the lowest of any county in the United States; 11% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Union County and Davie County.