| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 62,453 | 83,050 | 150,090 | |
| 2020 | R | 63,095 | 80,930 | 148,186 | |
| 2016 | R | 47,077 | 77,860 | 131,596 | |
| 2012 | R | 49,729 | 72,911 | 125,954 | |
| 2008 | R | 48,552 | 71,751 | 123,295 | |
| 2004 | R | 39,685 | 71,565 | 112,728 | |
| 2000 | R | 35,665 | 52,862 | 91,424 | |
| 1996 | R | 29,779 | 39,686 | 78,191 | |
| 1992 | R | 27,164 | 36,350 | 80,687 | |
| 1988 | R | 19,803 | 38,493 | 58,566 | |
| 1984 | R | 17,133 | 37,382 | 54,642 | |
| 1980 | R | 20,042 | 26,713 | 50,941 | |
| 1976 | R | 19,890 | 24,309 | 44,199 | |
| 1972 | R | 8,737 | 25,141 | 34,366 | |
| 1968 | R | 9,914 | 15,799 | 30,691 | |
| 1964 | D | 13,550 | 9,968 | 23,518 | |
| 1960 | R | 9,293 | 12,090 | 21,383 | |
| 1956 | R | 6,588 | 12,657 | 19,245 | |
| 1952 | R | 6,809 | 10,770 | 17,659 | |
| 1948 | R | 5,494 | 6,168 | 11,750 | |
| 1944 | R | 4,839 | 6,751 | 11,590 | |
| 1940 | R | 5,500 | 6,501 | 12,060 | |
| 1936 | D | 6,165 | 5,327 | 11,531 | |
| 1932 | D | 6,073 | 3,954 | 10,134 | |
| 1928 | R | 3,506 | 6,479 | 10,040 | |
| 1924 | D | 3,841 | 3,545 | 7,758 | |
| 1920 | R | 4,134 | 4,175 | 8,374 | |
| 1916 | D | 3,345 | 2,302 | 5,732 | |
| 1912 | D | 5,972 | 1,737 | 5,713 | |
| 1908 | D | 5,833 | 3,148 | 82 | |
| 1904 | D | 6,924 | 2,561 | 121 | |
| 1900 | D | 3,509 | 3,145 | 20 | |
| 1896 | R | 3,360 | 3,374 | 7,105 | |
| 1892 | D | 3,309 | 2,449 | 6,022 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Harford County sits at the northeastern edge of the Baltimore metro, where lower-density development and a large military presence around Aberdeen Proving Ground have anchored consistently Republican margins in statewide and national contests.
The Republican margin in Harford County reached its widest at forty-eight points in 1972. The margin in 2024 was fourteen points, in line with the county's deep historical pattern.
Harford County's loyalty is rooted in its place. Median household income of $112,265, a 73% non-Hispanic-white share, and a population of 263,757 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 Carroll County and Campbell County.