| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 957 | 2,711 | 3,739 | |
| 2020 | R | 1,120 | 2,615 | 3,804 | |
| 2016 | R | 1,201 | 2,296 | 3,784 | |
| 2012 | R | 1,791 | 1,947 | 3,833 | |
| 2008 | R | 1,986 | 2,020 | 4,102 | |
| 2004 | R | 1,859 | 2,088 | 4,011 | |
| 2000 | R | 1,674 | 1,903 | 3,709 | |
| 1996 | D | 1,846 | 1,287 | 3,623 | |
| 1992 | D | 1,866 | 1,316 | 3,986 | |
| 1988 | D | 2,192 | 1,406 | 3,627 | |
| 1984 | R | 2,098 | 2,104 | 4,242 | |
| 1980 | R | 2,048 | 2,212 | 4,640 | |
| 1976 | D | 2,698 | 1,932 | 4,707 | |
| 1972 | R | 1,880 | 2,638 | 4,593 | |
| 1968 | R | 2,057 | 2,261 | 4,588 | |
| 1964 | D | 3,331 | 1,542 | 4,885 | |
| 1960 | R | 2,411 | 3,039 | 5,457 | |
| 1956 | R | 2,806 | 2,912 | 5,725 | |
| 1952 | R | 2,521 | 3,621 | 6,168 | |
| 1948 | D | 3,172 | 2,547 | 5,803 | |
| 1944 | D | 3,316 | 2,934 | 6,268 | |
| 1940 | D | 3,938 | 3,494 | 7,448 | |
| 1936 | D | 4,131 | 3,327 | 7,494 | |
| 1932 | D | 3,591 | 2,148 | 5,830 | |
| 1928 | R | 2,675 | 3,942 | 6,675 | |
| 1924 | R | 1,693 | 3,221 | 6,835 | |
| 1920 | R | 2,592 | 4,187 | 6,845 | |
| 1916 | D | 2,111 | 1,962 | 4,135 | |
| 1912 | D | 1,659 | 1,351 | 3,928 | |
| 1908 | R | 1,809 | 2,149 | 4,091 | |
| 1904 | R | 1,548 | 2,430 | 4,158 | |
| 1900 | R | 2,058 | 2,415 | 4,539 | |
| 1896 | D | 2,362 | 2,268 | 4,680 | |
| 1892 | R | 1,486 | 1,856 | 3,780 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Decatur County's small population and agricultural economy mirror the broader rural Iowa shift toward wide Republican margins — the 2024 gap of nearly 47 points reflects a voting pattern that has grown steadily since 2000.
The Democratic margin in Decatur County peaked at thirty-seven points in 1964. By 2000 the county had flipped, voting Republican for the first time in many years. The 2024 margin was forty-seven points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Decatur County's median household income of $59,044 sits well below state and national norms, and 15% 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 Monroe County and Greene County.