| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 7,134 | 9,815 | 17,270 | |
| 2020 | R | 8,176 | 9,571 | 18,136 | |
| 2016 | R | 7,652 | 9,146 | 18,175 | |
| 2012 | D | 10,257 | 8,472 | 19,064 | |
| 2008 | D | 10,023 | 8,278 | 18,657 | |
| 2004 | R | 9,443 | 9,557 | 19,164 | |
| 2000 | R | 8,322 | 8,785 | 17,624 | |
| 1996 | D | 8,669 | 7,017 | 17,324 | |
| 1992 | D | 8,303 | 6,784 | 18,289 | |
| 1988 | D | 9,760 | 7,657 | 17,549 | |
| 1984 | R | 8,809 | 10,839 | 19,840 | |
| 1980 | R | 7,114 | 10,707 | 19,626 | |
| 1976 | R | 8,695 | 9,562 | 18,630 | |
| 1972 | R | 6,618 | 10,798 | 17,744 | |
| 1968 | R | 6,362 | 9,402 | 16,686 | |
| 1964 | D | 9,815 | 6,323 | 16,176 | |
| 1960 | R | 6,761 | 10,265 | 17,042 | |
| 1956 | R | 5,755 | 10,305 | 16,425 | |
| 1952 | R | 5,314 | 11,135 | 16,890 | |
| 1948 | R | 5,602 | 6,698 | 12,833 | |
| 1944 | R | 5,598 | 7,325 | 13,157 | |
| 1940 | R | 6,497 | 8,503 | 15,065 | |
| 1936 | R | 6,297 | 7,377 | 14,008 | |
| 1932 | R | 6,385 | 6,604 | 13,483 | |
| 1928 | R | 3,384 | 9,326 | 12,792 | |
| 1924 | R | 1,516 | 9,010 | 13,233 | |
| 1920 | R | 2,166 | 9,334 | 11,800 | |
| 1916 | R | 2,414 | 4,172 | 6,916 | |
| 1912 | D | 2,162 | 926 | 6,717 | |
| 1908 | R | 1,941 | 3,887 | 6,337 | |
| 1904 | R | 1,203 | 4,229 | 6,337 | |
| 1900 | R | 2,329 | 4,878 | 7,496 | |
| 1896 | R | 2,626 | 4,541 | 7,342 | |
| 1892 | R | 2,312 | 3,441 | 6,080 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Marshall County's population centers on Marshalltown, a meatpacking hub with one of Iowa's largest Latino immigrant communities, yet the county has moved roughly 20 points toward Republicans over the past two presidential cycles.
The Democratic margin in Marshall County has rarely exceeded twenty-two points in modern history; the Republican margin has rarely exceeded sixty-one points. 2024 delivered the county to the Republican candidate by sixteen points.
Marshall County's demographics resemble the country more than they resemble most counties. A 71% non-Hispanic-white share, a 11% poverty rate, and a median household income of $73,315 — all within the broad national range. The county's voting pattern over the last decade is most similar to that of Poweshiek County and Conejos County.