| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 2,245 | 5,566 | 7,959 | |
| 2020 | R | 2,440 | 5,569 | 8,155 | |
| 2016 | R | 2,131 | 4,902 | 7,552 | |
| 2012 | R | 3,136 | 4,065 | 7,322 | |
| 2008 | R | 3,555 | 3,909 | 7,578 | |
| 2004 | R | 2,906 | 4,680 | 7,680 | |
| 2000 | R | 2,551 | 3,802 | 6,543 | |
| 1996 | R | 2,576 | 3,070 | 6,527 | |
| 1992 | R | 2,349 | 2,763 | 6,868 | |
| 1988 | R | 2,883 | 3,108 | 6,027 | |
| 1984 | R | 2,495 | 4,352 | 6,882 | |
| 1980 | R | 2,152 | 4,502 | 7,053 | |
| 1976 | R | 3,228 | 3,489 | 6,790 | |
| 1972 | R | 2,369 | 4,721 | 7,171 | |
| 1968 | R | 2,410 | 3,867 | 6,825 | |
| 1964 | D | 4,575 | 3,203 | 7,787 | |
| 1960 | R | 3,613 | 4,940 | 8,562 | |
| 1956 | R | 3,709 | 5,209 | 8,935 | |
| 1952 | R | 3,370 | 5,972 | 9,366 | |
| 1948 | D | 4,608 | 4,341 | 9,016 | |
| 1944 | R | 4,201 | 5,059 | 9,309 | |
| 1940 | R | 5,317 | 6,094 | 11,428 | |
| 1936 | D | 6,206 | 5,314 | 11,678 | |
| 1932 | D | 7,427 | 3,513 | 11,008 | |
| 1928 | R | 4,406 | 5,605 | 10,046 | |
| 1924 | R | 3,179 | 5,062 | 9,924 | |
| 1920 | R | 3,479 | 6,127 | 9,742 | |
| 1916 | D | 2,932 | 2,610 | 5,689 | |
| 1912 | D | 2,157 | 1,528 | 5,321 | |
| 1908 | R | 2,425 | 2,914 | 5,561 | |
| 1904 | R | 1,696 | 3,364 | 5,421 | |
| 1900 | R | 2,837 | 3,303 | 6,291 | |
| 1896 | D | 3,214 | 2,839 | 6,108 | |
| 1892 | R | 2,200 | 2,302 | 5,110 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Harrison County, tucked along the Missouri River in western Iowa, has shifted steadily toward lopsided Republican margins over the past two decades, with its 2024 presidential gap of 41.7 points reflecting a broader rural consolidation pattern across the western tier of the state.
The Republican margin in Harrison County reached its widest at forty-two points in 2024. The margin in 2024 was forty-two points, in line with the county's deep historical pattern.
Harrison County's loyalty is rooted in its place. Median household income of $79,535, a 95% non-Hispanic-white share, and a population of 14,632 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 Griggs County and Walsh County.