| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 784 | 3,582 | 4,404 | |
| 2020 | R | 799 | 3,585 | 4,437 | |
| 2016 | R | 780 | 3,462 | 4,428 | |
| 2012 | R | 1,212 | 3,030 | 4,374 | |
| 2008 | R | 1,580 | 3,006 | 4,740 | |
| 2004 | R | 1,561 | 3,172 | 4,808 | |
| 2000 | R | 1,563 | 2,976 | 4,708 | |
| 1996 | D | 2,073 | 1,883 | 4,698 | |
| 1992 | D | 1,968 | 1,749 | 5,105 | |
| 1988 | R | 2,052 | 2,668 | 4,732 | |
| 1984 | R | 1,861 | 3,156 | 5,017 | |
| 1980 | R | 2,064 | 2,890 | 5,106 | |
| 1976 | R | 2,597 | 2,646 | 5,273 | |
| 1972 | R | 1,428 | 3,969 | 5,397 | |
| 1968 | R | 1,976 | 3,213 | 5,608 | |
| 1964 | D | 3,363 | 2,411 | 5,774 | |
| 1960 | R | 2,415 | 4,422 | 6,837 | |
| 1956 | R | 2,752 | 4,139 | 6,891 | |
| 1952 | R | 2,747 | 4,790 | 7,555 | |
| 1948 | R | 3,177 | 3,331 | 6,512 | |
| 1944 | R | 2,997 | 4,158 | 7,167 | |
| 1940 | R | 3,813 | 4,558 | 8,404 | |
| 1936 | R | 4,187 | 4,521 | 8,763 | |
| 1932 | D | 4,006 | 2,953 | 7,020 | |
| 1928 | R | 2,332 | 5,226 | 7,604 | |
| 1924 | R | 2,367 | 3,782 | 7,467 | |
| 1920 | R | 2,721 | 5,123 | 7,973 | |
| 1916 | R | 1,789 | 2,481 | 4,374 | |
| 1912 | D | 1,310 | 1,051 | 3,917 | |
| 1908 | R | 1,359 | 2,407 | 3,838 | |
| 1904 | R | 1,195 | 2,596 | 3,866 | |
| 1900 | R | 1,532 | 2,576 | 4,181 | |
| 1896 | R | 1,675 | 2,778 | 4,477 | |
| 1892 | R | 1,375 | 2,468 | 4,065 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Grundy County's small, agriculture-rooted population has shifted steadily toward outsized Republican margins over the past decade, with 2024's R+63.5 result placing it among the most one-sided counties in the state.
The Democratic margin in Grundy County peaked at sixteen points in 1964. By 2000 the county had flipped, voting Republican for the first time in many years. The 2024 margin was sixty-four points, the most Republican-leaning result in the county's modern history.
The economic context is the key. Grundy County's median household income of $51,975 sits well below state and national norms, and 18% 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 Carroll County and Dawson County.