| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 131,128 | 90,203 | 228,712 | |
| 2020 | D | 142,863 | 81,222 | 228,056 | |
| 2016 | D | 113,144 | 71,721 | 196,442 | |
| 2012 | D | 103,331 | 74,458 | 180,195 | |
| 2008 | D | 93,435 | 67,621 | 162,446 | |
| 2004 | R | 61,271 | 69,776 | 132,063 | |
| 2000 | R | 44,745 | 52,788 | 100,511 | |
| 1996 | R | 33,462 | 39,292 | 78,443 | |
| 1992 | R | 26,486 | 35,432 | 75,680 | |
| 1988 | R | 19,198 | 39,654 | 59,453 | |
| 1984 | R | 15,631 | 34,992 | 50,803 | |
| 1980 | R | 12,787 | 23,061 | 39,119 | |
| 1976 | R | 15,215 | 15,446 | 31,524 | |
| 1972 | R | 1,585 | 3,199 | 4,850 | |
| 1968 | R | 5,566 | 7,944 | 18,686 | |
| 1964 | R | 1,512 | 2,545 | 4,064 | |
| 1960 | D | 2,987 | 2,624 | 5,639 | |
| 1956 | R | 1,851 | 2,023 | 3,970 | |
| 1952 | D | 1,653 | 1,619 | 3,295 | |
| 1948 | D | 1,162 | 760 | 2,083 | |
| 1944 | D | 1,340 | 763 | 2,108 | |
| 1940 | D | 1,435 | 500 | 1,940 | |
| 1936 | D | 1,512 | 457 | 1,982 | |
| 1932 | D | 1,499 | 386 | 1,907 | |
| 1928 | D | 826 | 817 | 1,643 | |
| 1924 | D | 847 | 269 | 1,170 | |
| 1920 | D | 786 | 393 | 1,181 | |
| 1916 | D | 754 | 192 | 950 | |
| 1912 | D | 814 | 82 | 1,000 | |
| 1908 | D | 738 | 200 | 949 | |
| 1904 | D | 724 | 228 | 958 | |
| 1900 | D | 1,351 | 680 | 2,031 | |
| 1896 | D | 1,341 | 727 | 2,077 | |
| 1892 | D | 1,356 | 663 | 2,057 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Prince William's rapid demographic transformation — driven by a surge in immigrant and college-educated residents along the I-95 corridor — has shifted its presidential margin from single digits to D+18 in roughly two decades.
The 2008 election was the turning point, when the Democratic candidate carried the county by sixteen points. The 2024 margin was eighteen points, in line with the county's new direction.
The demographics suggest why. A population of 488,880, a 43% non-Hispanic-white share, and a median household income of $131,402 situate the county in the broader realignment patterns of recent cycles. The county's voting pattern over the last decade is most similar to that of Manassas Park city and Henrico County.
