| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 4,297 | 7,119 | 11,588 | |
| 2020 | R | 4,561 | 6,971 | 11,765 | |
| 2016 | R | 3,943 | 6,173 | 11,092 | |
| 2012 | R | 5,115 | 5,562 | 11,004 | |
| 2008 | R | 5,170 | 5,247 | 10,626 | |
| 2004 | R | 4,595 | 5,977 | 10,688 | |
| 2000 | R | 3,932 | 4,827 | 9,094 | |
| 1996 | D | 3,828 | 3,600 | 8,173 | |
| 1992 | R | 3,384 | 3,576 | 9,018 | |
| 1988 | D | 3,776 | 3,741 | 7,616 | |
| 1984 | R | 3,079 | 4,613 | 7,770 | |
| 1980 | R | 2,877 | 3,967 | 7,627 | |
| 1976 | R | 3,448 | 4,218 | 7,807 | |
| 1972 | R | 2,784 | 5,187 | 8,089 | |
| 1968 | R | 2,679 | 4,899 | 7,943 | |
| 1964 | D | 4,587 | 3,315 | 7,919 | |
| 1960 | R | 3,222 | 5,861 | 9,089 | |
| 1956 | R | 3,022 | 5,844 | 8,876 | |
| 1952 | R | 2,604 | 6,946 | 9,585 | |
| 1948 | R | 3,485 | 4,680 | 8,245 | |
| 1944 | R | 3,423 | 5,308 | 8,763 | |
| 1940 | R | 4,030 | 5,649 | 9,721 | |
| 1936 | R | 4,379 | 4,619 | 9,118 | |
| 1932 | D | 4,554 | 3,889 | 8,595 | |
| 1928 | R | 2,754 | 5,948 | 8,742 | |
| 1924 | R | 1,868 | 5,053 | 8,378 | |
| 1920 | R | 2,257 | 5,813 | 8,177 | |
| 1916 | R | 2,139 | 2,745 | 4,963 | |
| 1912 | D | 2,003 | 1,264 | 4,797 | |
| 1908 | R | 2,119 | 2,631 | 4,889 | |
| 1904 | R | 1,772 | 2,875 | 4,853 | |
| 1900 | R | 2,234 | 2,844 | 5,241 | |
| 1896 | R | 2,292 | 2,882 | 5,296 | |
| 1892 | R | 2,134 | 2,518 | 4,838 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Washington County sits in southeast Iowa along the English River, its electorate anchored by small-town and agricultural communities that have shifted steadily rightward over the past two decades, with the 2024 presidential margin reaching R+24.4.
The Republican margin in Washington County reached its widest at forty-five points in 1952. The margin in 2024 was twenty-four points, in line with the county's deep historical pattern.
Washington County's loyalty is rooted in its place. Median household income of $75,647, a 90% non-Hispanic-white share, and a population of 22,561 together describe a community whose political habits are deeply settled. The county's voting pattern over the last decade is most similar to that of Lyon County and Polk County.