| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 116,152 | 24,054 | 144,129 | |
| 2020 | D | 128,288 | 24,612 | 155,830 | |
| 2016 | D | 108,707 | 21,771 | 140,683 | |
| 2012 | D | 99,896 | 30,880 | 134,731 | |
| 2008 | D | 109,320 | 28,384 | 140,570 | |
| 2004 | D | 99,070 | 34,378 | 135,325 | |
| 2000 | D | 79,135 | 34,872 | 123,155 | |
| 1996 | D | 67,406 | 32,714 | 116,140 | |
| 1992 | D | 76,158 | 30,479 | 130,707 | |
| 1988 | D | 69,394 | 46,855 | 117,920 | |
| 1984 | D | 57,533 | 56,887 | 116,050 | |
| 1980 | R | 39,231 | 49,678 | 108,507 | |
| 1976 | R | 43,590 | 53,425 | 101,715 | |
| 1972 | R | 47,414 | 54,123 | 103,883 | |
| 1968 | R | 36,278 | 41,422 | 82,755 | |
| 1964 | D | 46,462 | 28,682 | 75,364 | |
| 1960 | R | 27,888 | 37,620 | 65,665 | |
| 1956 | R | 17,301 | 33,792 | 51,244 | |
| 1952 | R | 14,236 | 29,574 | 44,278 | |
| 1948 | R | 12,540 | 18,747 | 32,855 | |
| 1944 | D | 14,516 | 13,304 | 27,896 | |
| 1940 | D | 11,365 | 10,974 | 22,640 | |
| 1936 | D | 12,152 | 6,211 | 18,572 | |
| 1932 | D | 9,764 | 6,480 | 16,996 | |
| 1928 | R | 5,686 | 7,862 | 13,688 | |
| 1924 | R | 656 | 5,780 | 10,800 | |
| 1920 | R | 1,688 | 5,375 | 7,813 | |
| 1916 | R | 3,789 | 4,328 | 8,647 | |
| 1912 | D | 2,849 | 0 | 6,400 | |
| 1908 | R | 983 | 2,732 | 4,003 | |
| 1904 | R | 772 | 2,199 | 3,110 | |
| 1900 | R | 904 | 1,681 | 2,644 | |
| 1896 | R | 874 | 1,448 | 2,358 | |
| 1892 | R | 949 | 1,186 | 2,213 | |
| 1888 | R | 802 | 936 | 1,774 | |
| 1884 | R | 727 | 851 | 1,587 | |
| 1880 | R | 561 | 761 | 1,345 | |
| 1876 | R | 619 | 651 | 1,270 |
Marin County's D+63.9 margin in 2024 places it among the most heavily Democratic counties in the country, a pattern sustained by high educational attainment and coastal affluence that have long defined its electorate.
The unraveling was not abrupt. The Democratic margin in Marin County peaked at sixty-seven points in 2020; it narrowed steadily over the late twentieth century. The 1984 election delivered the county to the Republican party for the first time in many years, by a margin of one points. By 2024, the margin had widened further.
The economic and demographic context is severe. Marin County's median household income of $149,091 is among the lowest of any county in the United States; 8% of residents live below the federal poverty line. The county's voting pattern over the last decade is most similar to that of Denver County and Dane County.
