| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 9,143 | 16,997 | 26,589 | |
| 2020 | R | 9,626 | 16,523 | 26,756 | |
| 2016 | R | 8,065 | 13,454 | 23,237 | |
| 2012 | R | 9,451 | 11,343 | 21,313 | |
| 2008 | D | 11,063 | 10,687 | 22,171 | |
| 2004 | R | 8,463 | 11,198 | 19,831 | |
| 2000 | R | 7,516 | 8,709 | 16,584 | |
| 1996 | D | 6,759 | 6,177 | 14,902 | |
| 1992 | R | 6,122 | 6,346 | 16,265 | |
| 1988 | R | 5,525 | 8,743 | 14,361 | |
| 1984 | R | 4,671 | 9,595 | 14,325 | |
| 1980 | R | 3,970 | 8,397 | 13,204 | |
| 1976 | R | 5,534 | 7,581 | 13,201 | |
| 1972 | R | 3,584 | 8,725 | 12,341 | |
| 1968 | R | 3,407 | 6,607 | 11,105 | |
| 1964 | R | 5,246 | 5,522 | 10,768 | |
| 1960 | R | 4,276 | 6,948 | 11,228 | |
| 1956 | R | 2,618 | 7,640 | 10,261 | |
| 1952 | R | 3,118 | 7,347 | 10,478 | |
| 1948 | R | 3,255 | 5,954 | 9,240 | |
| 1944 | R | 3,544 | 6,310 | 9,876 | |
| 1940 | R | 4,105 | 6,593 | 10,741 | |
| 1936 | R | 4,481 | 5,360 | 10,185 | |
| 1932 | D | 4,755 | 4,491 | 9,315 | |
| 1928 | R | 3,174 | 5,126 | 8,329 | |
| 1924 | R | 742 | 4,337 | 6,780 | |
| 1920 | R | 803 | 4,647 | 5,805 | |
| 1916 | R | 2,241 | 4,811 | 7,247 | |
| 1912 | R | 1,172 | 1,380 | 4,731 | |
| 1908 | R | 1,359 | 3,127 | 4,957 | |
| 1904 | R | 841 | 3,448 | 4,945 | |
| 1900 | R | 1,687 | 3,735 | 5,702 | |
| 1896 | R | 2,074 | 3,246 | 5,439 | |
| 1892 | R | 1,892 | 2,159 | 4,296 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
Grundy County, anchored by Morris along the Illinois River, shifted from a competitive industrial belt to an R+29.5 result in 2024—a trajectory that mirrors the broader realignment of working-class exurban counties across the Midwest.
The Republican margin in Grundy County reached its widest at sixty-six points in 1920. The margin in 2024 was thirty points, in line with the county's deep historical pattern.
Grundy County's loyalty is rooted in its place. Median household income of $92,235, a 86% non-Hispanic-white share, and a population of 53,219 together describe a community whose political habits are deeply settled. The county's voting pattern over the last decade is most similar to that of Oceana County and Mecosta County.
