| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 9,251 | 20,973 | 31,225 | |
| 2020 | R | 10,707 | 21,270 | 33,038 | |
| 2016 | R | 7,673 | 17,059 | 27,597 | |
| 2012 | R | 8,584 | 15,499 | 24,969 | |
| 2008 | R | 9,484 | 15,254 | 25,523 | |
| 2004 | R | 8,884 | 17,068 | 26,322 | |
| 2000 | R | 7,809 | 14,140 | 23,060 | |
| 1996 | R | 8,774 | 9,703 | 21,495 | |
| 1992 | R | 6,787 | 7,095 | 19,643 | |
| 1988 | R | 8,327 | 10,254 | 18,981 | |
| 1984 | R | 8,246 | 14,211 | 22,514 | |
| 1980 | R | 7,382 | 12,950 | 22,414 | |
| 1976 | R | 7,985 | 9,345 | 18,031 | |
| 1972 | R | 6,090 | 10,470 | 18,071 | |
| 1968 | R | 6,402 | 8,975 | 16,379 | |
| 1964 | D | 10,689 | 6,138 | 16,859 | |
| 1960 | R | 8,053 | 9,374 | 17,433 | |
| 1956 | R | 7,678 | 9,654 | 17,332 | |
| 1952 | R | 7,098 | 10,529 | 17,667 | |
| 1948 | D | 5,891 | 5,726 | 11,761 | |
| 1944 | R | 4,967 | 5,379 | 10,391 | |
| 1940 | R | 4,935 | 5,193 | 10,160 | |
| 1936 | D | 5,753 | 2,943 | 9,411 | |
| 1932 | D | 5,631 | 2,930 | 8,877 | |
| 1928 | R | 2,390 | 5,277 | 7,780 | |
| 1924 | R | 3,052 | 3,854 | 8,620 | |
| 1920 | R | 3,255 | 4,979 | 8,580 | |
| 1916 | D | 4,606 | 3,664 | 8,655 | |
| 1912 | D | 1,563 | 1,261 | 4,304 | |
| 1908 | R | 1,568 | 2,328 | 4,185 | |
| 1904 | R | 840 | 2,642 | 3,987 | |
| 1900 | R | 1,638 | 1,975 | 3,794 | |
| 1896 | D | 2,083 | 1,859 | 4,001 | |
| 1892 | R | 398 | 1,446 | 3,432 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Umatilla County anchors Oregon's agricultural southeast, where wheat farming and food-processing industries shape a voting pattern that ran nearly 40 points to the right of the state's statewide result in 2024.
The Democratic margin in Umatilla County peaked at thirty points in 1932. By 1968 the county had flipped, voting Republican for the first time in many years. The 2024 margin was thirty-eight points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Umatilla County's median household income of $67,728 sits well below state and national norms, and 12% of residents live below the federal poverty line. The shift here is part of a broader realignment of working-class places across the country. The county's voting pattern over the last decade is most similar to that of Shelby County and Stillwater County.