| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 5,895 | 9,199 | 15,403 | |
| 2020 | R | 6,303 | 8,695 | 15,340 | |
| 2016 | R | 5,541 | 7,484 | 14,310 | |
| 2012 | D | 7,512 | 6,556 | 14,388 | |
| 2008 | D | 7,356 | 6,293 | 13,929 | |
| 2004 | D | 7,027 | 6,870 | 14,009 | |
| 2000 | D | 6,270 | 5,625 | 12,249 | |
| 1996 | D | 6,446 | 4,293 | 11,835 | |
| 1992 | D | 5,913 | 4,148 | 12,219 | |
| 1988 | D | 7,232 | 4,381 | 11,686 | |
| 1984 | D | 6,485 | 5,746 | 12,277 | |
| 1980 | R | 5,126 | 5,732 | 12,087 | |
| 1976 | D | 6,595 | 5,413 | 12,263 | |
| 1972 | R | 5,057 | 6,271 | 11,551 | |
| 1968 | R | 5,219 | 5,260 | 11,096 | |
| 1964 | D | 7,699 | 3,543 | 11,335 | |
| 1960 | R | 5,759 | 6,761 | 12,527 | |
| 1956 | R | 5,815 | 6,740 | 12,564 | |
| 1952 | R | 4,896 | 7,901 | 12,947 | |
| 1948 | D | 5,541 | 4,183 | 10,222 | |
| 1944 | D | 6,062 | 4,868 | 11,003 | |
| 1940 | D | 7,168 | 5,227 | 12,469 | |
| 1936 | D | 7,080 | 4,110 | 11,629 | |
| 1932 | D | 5,293 | 3,694 | 9,722 | |
| 1928 | R | 3,049 | 7,521 | 10,742 | |
| 1924 | R | 702 | 4,980 | 10,928 | |
| 1920 | R | 2,240 | 7,093 | 9,980 | |
| 1916 | R | 2,338 | 2,955 | 5,638 | |
| 1912 | D | 1,601 | 802 | 5,880 | |
| 1908 | R | 1,958 | 3,368 | 5,836 | |
| 1904 | R | 1,148 | 3,830 | 5,833 | |
| 1900 | R | 2,264 | 4,151 | 6,741 | |
| 1896 | R | 2,801 | 3,741 | 6,630 | |
| 1892 | R | 1,925 | 2,959 | 5,163 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Boone County, anchored by its small county-seat city, backed Republican presidential candidates by double digits throughout the 2010s before widening that margin to R+21.4 in 2024, reflecting broader rural Iowa realignment.
The county's recent history is a story of close margins. The Democratic margin reached thirty-seven points in 1964; the Republican margin reached forty-nine points in 1920. Most other elections have been decided by single-digit points.
Boone County's demographics — a population of 26,668, a 94% non-Hispanic-white share, a median household income of $83,531 — situate the county close to national averages on several dimensions. The county's voting pattern over the last decade is most similar to that of Wapello County and Cowlitz County.
