| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 90,324 | 75,271 | 169,536 | |
| 2020 | D | 89,165 | 73,764 | 166,786 | |
| 2016 | D | 67,086 | 64,428 | 144,235 | |
| 2012 | D | 70,203 | 69,137 | 142,133 | |
| 2008 | D | 70,277 | 64,334 | 137,059 | |
| 2004 | R | 61,395 | 65,751 | 128,449 | |
| 2000 | R | 49,637 | 51,502 | 107,009 | |
| 1996 | D | 45,119 | 31,219 | 88,057 | |
| 1992 | D | 35,820 | 26,568 | 85,499 | |
| 1988 | D | 34,952 | 30,850 | 66,415 | |
| 1984 | R | 28,527 | 29,046 | 57,942 | |
| 1980 | D | 25,634 | 22,718 | 54,902 | |
| 1976 | D | 26,454 | 20,716 | 48,583 | |
| 1972 | R | 16,102 | 19,142 | 36,098 | |
| 1968 | D | 16,449 | 10,921 | 28,954 | |
| 1964 | D | 18,108 | 8,850 | 27,022 | |
| 1960 | D | 11,870 | 11,202 | 23,133 | |
| 1956 | R | 7,462 | 9,562 | 17,056 | |
| 1952 | R | 7,768 | 9,408 | 17,240 | |
| 1948 | D | 8,039 | 5,686 | 13,970 | |
| 1944 | R | 5,599 | 6,014 | 11,679 | |
| 1940 | R | 6,288 | 6,710 | 13,052 | |
| 1936 | D | 6,768 | 3,863 | 11,710 | |
| 1932 | D | 6,413 | 3,996 | 10,656 | |
| 1928 | R | 4,158 | 6,113 | 10,351 | |
| 1924 | R | 699 | 4,482 | 8,553 | |
| 1920 | R | 1,558 | 5,852 | 7,819 | |
| 1916 | R | 1,610 | 2,167 | 4,047 | |
| 1912 | D | 1,289 | 581 | 4,223 | |
| 1908 | R | 1,120 | 2,727 | 3,981 | |
| 1904 | R | 652 | 2,913 | 3,644 | |
| 1900 | R | 1,279 | 2,984 | 4,357 | |
| 1896 | R | 1,558 | 3,995 | 5,666 | |
| 1892 | D | 2,451 | 1,733 | 4,598 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Washington County sits along the St. Croix River east of St. Paul, where steady population growth and a mix of established suburbs and newer exurban development have kept its presidential margins consistently single-digit Democratic over the past several cycles.
The Democratic margin in Washington County has rarely exceeded thirty-four points in modern history; the Republican margin has rarely exceeded sixty-two points. 2024 delivered the county to the Democratic candidate by nine points.
Washington County's demographics resemble the country more than they resemble most counties. A 78% non-Hispanic-white share, a 5% poverty rate, and a median household income of $115,345 — all within the broad national range. The county's voting pattern over the last decade is most similar to that of Dakota County and Clark County.