| Year | Won | Margin | Democratic | Republican | Total |
|---|---|---|---|---|---|
| 2024 | R | 479 | 2,223 | 2,752 | |
| 2020 | R | 564 | 2,364 | 3,003 | |
| 2016 | R | 490 | 2,050 | 2,820 | |
| 2012 | R | 943 | 1,678 | 2,712 | |
| 2008 | R | 981 | 1,374 | 2,416 | |
| 2004 | R | 1,030 | 1,744 | 2,820 | |
| 2000 | R | 888 | 1,682 | 2,737 | |
| 1996 | R | 1,096 | 1,187 | 2,756 | |
| 1992 | R | 1,173 | 1,321 | 3,396 | |
| 1988 | R | 1,665 | 1,888 | 3,583 | |
| 1984 | R | 1,283 | 2,485 | 3,801 | |
| 1980 | R | 939 | 2,922 | 4,104 | |
| 1976 | R | 1,994 | 2,043 | 4,111 | |
| 1972 | R | 1,554 | 2,765 | 4,346 | |
| 1968 | R | 1,595 | 2,226 | 4,106 | |
| 1964 | D | 2,643 | 1,728 | 4,379 | |
| 1960 | R | 2,231 | 2,715 | 4,948 | |
| 1956 | R | 1,825 | 3,019 | 4,860 | |
| 1952 | R | 1,228 | 4,227 | 5,518 | |
| 1948 | R | 1,770 | 2,578 | 4,567 | |
| 1944 | R | 1,934 | 3,141 | 5,112 | |
| 1940 | R | 2,225 | 3,894 | 6,174 | |
| 1936 | D | 3,294 | 1,619 | 6,169 | |
| 1932 | D | 3,937 | 1,396 | 5,566 | |
| 1928 | R | 2,535 | 2,914 | 5,494 | |
| 1924 | R | 264 | 1,692 | 4,587 | |
| 1920 | R | 848 | 3,534 | 4,770 | |
| 1916 | D | 1,316 | 692 | 2,209 | |
| 1912 | D | 959 | 589 | 2,495 | |
| 1908 | R | 1,296 | 1,772 | 3,155 | |
| 1904 | R | 556 | 1,807 | 2,457 | |
| 1900 | R | 222 | 595 | 850 | |
| 1896 | R | 166 | 217 | 384 | |
| 1892 | R | 0 | 201 | 313 | |
| 1888 | — | — | — | — | |
| 1884 | — | — | — | — | |
| 1880 | — | — | — | — | |
| 1876 | — | — | — | — |
With under 6,000 residents spread across a vast agricultural landscape, McHenry County has delivered lopsided Republican presidential margins for decades, hitting R+63.4 in 2024 — a pattern typical of the state's sparsely populated northern plains counties.
The Republican margin in McHenry County reached its widest at sixty-four points in 1892. The margin in 2024 was sixty-three points, in line with the county's deep historical pattern.
McHenry County's loyalty is rooted in its place. Median household income of $80,733, a 94% non-Hispanic-white share, and a population of 5,207 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 Renville County and McLean County.