| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 4,896 | 9,479 | 14,583 | |
| 2020 | R | 5,821 | 9,516 | 15,633 | |
| 2016 | R | 5,594 | 8,715 | 15,277 | |
| 2012 | D | 8,663 | 6,789 | 15,770 | |
| 2008 | D | 8,820 | 6,663 | 15,931 | |
| 2004 | D | 9,125 | 7,403 | 16,707 | |
| 2000 | D | 8,355 | 6,313 | 15,139 | |
| 1996 | D | 8,437 | 4,828 | 14,770 | |
| 1992 | D | 8,670 | 4,852 | 16,083 | |
| 1988 | D | 10,177 | 5,350 | 15,673 | |
| 1984 | D | 10,545 | 7,098 | 17,800 | |
| 1980 | D | 8,923 | 7,475 | 17,668 | |
| 1976 | D | 10,249 | 6,786 | 17,268 | |
| 1972 | R | 8,348 | 9,301 | 18,171 | |
| 1968 | D | 9,375 | 7,825 | 18,647 | |
| 1964 | D | 13,971 | 5,524 | 19,546 | |
| 1960 | D | 11,116 | 11,036 | 22,167 | |
| 1956 | D | 10,960 | 10,401 | 21,381 | |
| 1952 | R | 10,449 | 11,571 | 22,150 | |
| 1948 | D | 10,841 | 7,875 | 18,976 | |
| 1944 | D | 10,732 | 8,244 | 19,089 | |
| 1940 | D | 11,880 | 9,039 | 21,006 | |
| 1936 | D | 10,578 | 7,647 | 18,512 | |
| 1932 | D | 9,504 | 7,256 | 17,076 | |
| 1928 | R | 5,793 | 11,586 | 17,528 | |
| 1924 | R | 3,039 | 9,870 | 17,329 | |
| 1920 | R | 4,131 | 9,884 | 14,537 | |
| 1916 | R | 3,994 | 4,398 | 9,229 | |
| 1912 | D | 3,102 | 2,755 | 8,470 | |
| 1908 | R | 3,724 | 4,541 | 8,959 | |
| 1904 | R | 2,473 | 4,912 | 8,105 | |
| 1900 | R | 3,902 | 4,742 | 8,912 | |
| 1896 | R | 4,041 | 4,319 | 8,510 | |
| 1892 | R | 3,380 | 3,643 | 7,804 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Wapello County, anchored by Ottumwa along the Des Moines River, was a union-labor stronghold that backed Democrats into the 2000s; by 2024 it recorded an R+31 presidential margin, tracing one of Iowa's steepest partisan realignments.
The 2016 election was the turning point, when the Republican candidate carried the county by twenty points. The 2024 margin was thirty-one points, in line with the county's new direction.
The demographics suggest why. A population of 35,362, a 79% non-Hispanic-white share, and a median household income of $64,766 situate the county in the broader realignment patterns of recent cycles. The county's voting pattern over the last decade is most similar to that of Boone County and Lee County.
