| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 386,438 | 181,895 | 589,427 | |
| 2020 | D | 419,943 | 168,401 | 600,823 | |
| 2016 | D | 355,133 | 157,710 | 551,183 | |
| 2012 | D | 315,273 | 206,773 | 529,287 | |
| 2008 | D | 310,359 | 200,994 | 516,254 | |
| 2004 | D | 245,671 | 211,980 | 461,379 | |
| 2000 | R | 196,501 | 202,181 | 413,775 | |
| 1996 | R | 170,150 | 176,033 | 365,263 | |
| 1992 | R | 160,186 | 170,488 | 385,218 | |
| 1988 | R | 125,711 | 200,641 | 328,365 | |
| 1984 | R | 107,295 | 183,181 | 291,298 | |
| 1980 | R | 73,734 | 137,620 | 239,705 | |
| 1976 | R | 92,037 | 110,424 | 205,957 | |
| 1972 | R | 54,844 | 112,135 | 169,246 | |
| 1968 | R | 44,796 | 57,462 | 117,319 | |
| 1964 | D | 48,680 | 30,755 | 79,517 | |
| 1960 | R | 26,064 | 28,006 | 54,219 | |
| 1956 | R | 15,633 | 20,761 | 37,267 | |
| 1952 | R | 8,329 | 13,020 | 21,379 | |
| 1948 | R | 3,719 | 4,930 | 9,489 | |
| 1944 | R | 3,582 | 4,046 | 7,662 | |
| 1940 | D | 3,263 | 2,371 | 5,660 | |
| 1936 | D | 2,913 | 1,584 | 4,527 | |
| 1932 | D | 2,714 | 1,368 | 4,154 | |
| 1928 | R | 1,229 | 2,507 | 3,736 | |
| 1924 | D | 1,586 | 765 | 2,550 | |
| 1920 | D | 1,598 | 987 | 2,617 | |
| 1916 | D | 1,179 | 472 | 1,666 | |
| 1912 | D | 992 | 187 | 1,338 | |
| 1908 | D | 1,143 | 404 | 1,560 | |
| 1904 | D | 774 | 422 | 1,211 | |
| 1900 | D | 2,135 | 1,507 | 3,656 | |
| 1896 | D | 2,109 | 1,877 | 4,016 | |
| 1892 | D | 2,168 | 1,537 | 3,730 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Fairfax County's rapid demographic shift—driven by federal-sector employment and immigration from Asia and Latin America—has moved it from a competitive suburb into one of the most reliably Democratic large counties in the mid-Atlantic.
The unraveling was not abrupt. The Democratic margin in Fairfax County peaked at sixty points in 1912; 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 seven points. By 2024, the margin had settled into deep Republican territory.
The economic and demographic context is severe. Fairfax County's median household income of $153,637 is among the lowest of any county in the United States; 6% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Fairfax city and Mecklenburg County.