| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | D | 130,578 | 106,386 | 246,237 | |
| 2020 | D | 139,043 | 110,509 | 257,679 | |
| 2016 | D | 102,095 | 88,392 | 214,039 | |
| 2012 | D | 95,493 | 88,592 | 189,332 | |
| 2008 | D | 103,476 | 83,595 | 191,878 | |
| 2004 | R | 95,129 | 97,691 | 195,000 | |
| 2000 | R | 76,421 | 77,539 | 162,262 | |
| 1996 | D | 67,709 | 59,443 | 145,146 | |
| 1992 | D | 60,310 | 53,724 | 154,538 | |
| 1988 | R | 59,799 | 61,381 | 123,351 | |
| 1984 | R | 47,254 | 68,630 | 116,173 | |
| 1980 | R | 40,462 | 54,111 | 109,483 | |
| 1976 | R | 42,504 | 47,671 | 93,959 | |
| 1972 | R | 32,540 | 41,767 | 78,089 | |
| 1968 | R | 27,939 | 32,363 | 63,961 | |
| 1964 | D | 35,711 | 21,299 | 57,043 | |
| 1960 | R | 23,679 | 28,531 | 52,319 | |
| 1956 | R | 20,416 | 25,314 | 45,730 | |
| 1952 | R | 16,219 | 24,174 | 40,620 | |
| 1948 | R | 14,263 | 14,431 | 30,083 | |
| 1944 | D | 14,060 | 12,492 | 26,987 | |
| 1940 | D | 13,547 | 11,416 | 25,153 | |
| 1936 | D | 14,203 | 5,830 | 21,303 | |
| 1932 | D | 11,575 | 5,964 | 18,608 | |
| 1928 | R | 5,918 | 9,216 | 15,486 | |
| 1924 | R | 3,099 | 5,864 | 13,548 | |
| 1920 | R | 3,740 | 6,928 | 11,639 | |
| 1916 | R | 5,334 | 6,349 | 12,471 | |
| 1912 | D | 2,171 | 1,503 | 6,532 | |
| 1908 | R | 1,866 | 2,776 | 5,149 | |
| 1904 | R | 684 | 2,783 | 4,106 | |
| 1900 | R | 1,641 | 2,234 | 4,148 | |
| 1896 | R | 2,386 | 2,664 | 5,144 | |
| 1892 | R | 655 | 1,815 | 4,078 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Clackamas has trended toward Democratic margins in recent cycles as Portland's suburbs densified, yet its rural eastern reaches—stretching to Mt. Hood—keep it measurably closer than neighboring Multnomah, with a 2024 presidential margin of D+9.8.
The county's recent history is a story of close margins. The Democratic margin reached thirty-nine points in 1936; the Republican margin reached fifty-one points in 1904. Most other elections have been decided by single-digit points.
Clackamas County's demographics — a population of 423,975, a 79% non-Hispanic-white share, a median household income of $103,517 — situate the county close to national averages on several dimensions. The county's voting pattern over the last decade is most similar to that of Champaign County and Jefferson County.
