| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Kendall County | 1 | 10.4% | 146,113 | 132,351 |
| Champaign County | 2 | 4.21% | 214,935 | 206,252 |
| Grundy County | 3 | 2.95% | 54,083 | 52,535 |
| McHenry County | 4 | 2.75% | 318,483 | 309,973 |
| Will County | 5 | 2.42% | 713,783 | 696,909 |
| DeKalb County | 6 | 1.63% | 102,009 | 100,368 |
| Kane County | 7 | 1.62% | 524,753 | 516,403 |
| DuPage County | 8 | 1.46% | 945,104 | 931,508 |
| Lake County | 9 | 1.34% | 723,001 | 713,426 |
| Brown County | 10 | 1.22% | 6,313 | 6,237 |
| Clinton County | 11 | 1.02% | 37,288 | 36,913 |
| Putnam County | 12 | 0.83% | 5,678 | 5,631 |
| McLean County | 13 | 0.82% | 172,645 | 171,236 |
| Douglas County | 14 | 0.68% | 19,915 | 19,780 |
| Ford County | 15 | 0.56% | 13,586 | 13,511 |
| Jackson County | 16 | 0.5% | 53,531 | 53,264 |
| Williamson County | 17 | 0.4% | 67,391 | 67,121 |
| Winnebago County | 18 | 0.14% | 285,366 | 284,963 |
| Effingham County | 19 | 0.13% | 34,751 | 34,707 |
| Boone County | 20 | 0.09% | 53,387 | 53,339 |
| Johnson County | 21 | -0.28% | 13,285 | 13,322 |
| Monroe County | 22 | -0.45% | 34,794 | 34,953 |
| Peoria County | 23 | -0.54% | 180,525 | 181,512 |
| Woodford County | 24 | -0.56% | 38,193 | 38,407 |
| Rock Island County | 25 | -0.58% | 143,523 | 144,360 |
| Moultrie County | 26 | -0.61% | 14,403 | 14,492 |
| Cook County | 27 | -0.84% | 5,222,712 | 5,267,072 |
| Piatt County | 28 | -0.88% | 16,536 | 16,683 |
| Sangamon County | 29 | -0.89% | 194,474 | 196,223 |
| Ogle County | 30 | -0.89% | 51,299 | 51,762 |
| Randolph County | 31 | -0.9% | 29,813 | 30,084 |
| Kankakee County | 32 | -0.9% | 106,434 | 107,403 |
| LaSalle County | 33 | -0.94% | 108,383 | 109,409 |
| Cumberland County | 34 | -0.95% | 10,338 | 10,437 |
| De Witt County | 35 | -1.02% | 15,307 | 15,464 |
| Livingston County | 36 | -1.08% | 35,429 | 35,816 |
| Crawford County | 37 | -1.09% | 18,434 | 18,637 |
| Wayne County | 38 | -1.11% | 15,981 | 16,161 |
| Tazewell County | 39 | -1.13% | 129,807 | 131,296 |
| Madison County | 40 | -1.19% | 262,592 | 265,749 |
| Logan County | 41 | -1.35% | 27,528 | 27,905 |
| Schuyler County | 42 | -1.38% | 6,775 | 6,870 |
| Whiteside County | 43 | -1.52% | 54,732 | 55,574 |
| Jersey County | 44 | -1.63% | 21,142 | 21,492 |
| Coles County | 45 | -1.64% | 46,314 | 47,084 |
| Washington County | 46 | -1.68% | 13,500 | 13,731 |
| Lee County | 47 | -1.71% | 33,482 | 34,063 |
| Fayette County | 48 | -1.77% | 21,105 | 21,485 |
| Pope County | 49 | -1.78% | 3,691 | 3,758 |
| Carroll County | 50 | -1.8% | 15,396 | 15,678 |
| Shelby County | 51 | -1.99% | 20,491 | 20,907 |
| Bond County | 52 | -2.02% | 16,515 | 16,856 |
| Stark County | 53 | -2.06% | 5,277 | 5,388 |
| Knox County | 54 | -2.08% | 48,769 | 49,806 |
| Franklin County | 55 | -2.14% | 36,910 | 37,717 |
| Marshall County | 56 | -2.19% | 11,454 | 11,710 |
| Union County | 57 | -2.27% | 16,906 | 17,298 |
| Christian County | 58 | -2.37% | 33,175 | 33,982 |
| Henry County | 59 | -2.41% | 47,992 | 49,178 |
| Jasper County | 60 | -2.45% | 9,028 | 9,255 |
| Cass County | 61 | -2.54% | 12,647 | 12,976 |
| St. Clair County | 62 | -2.67% | 250,204 | 257,070 |
| Edgar County | 63 | -2.7% | 16,354 | 16,808 |
| Montgomery County | 64 | -2.72% | 27,474 | 28,242 |
| McDonough County | 65 | -2.74% | 26,372 | 27,116 |
| Menard County | 66 | -2.79% | 11,930 | 12,272 |
| Adams County | 67 | -2.8% | 63,783 | 65,622 |
| Macoupin County | 68 | -2.81% | 43,663 | 44,924 |
| Macon County | 69 | -2.93% | 100,720 | 103,764 |
| Jefferson County | 70 | -3.02% | 35,883 | 37,000 |
| Hamilton County | 71 | -3.04% | 7,750 | 7,993 |
| Bureau County | 72 | -3.04% | 32,214 | 33,225 |
| Morgan County | 73 | -3.08% | 32,463 | 33,494 |
| Pike County | 74 | -3.14% | 14,177 | 14,637 |
| Iroquois County | 75 | -3.21% | 26,101 | 26,966 |
| Mercer County | 76 | -3.22% | 15,128 | 15,632 |
| Scott County | 77 | -3.23% | 4,910 | 5,074 |
| Clark County | 78 | -3.33% | 14,934 | 15,448 |
| Wabash County | 79 | -3.44% | 10,926 | 11,315 |
| Fulton County | 80 | -3.57% | 32,356 | 33,554 |
| Jo Daviess County | 81 | -3.58% | 21,307 | 22,098 |
| White County | 82 | -3.66% | 13,308 | 13,814 |
| Richland County | 83 | -3.69% | 15,222 | 15,805 |
| Warren County | 84 | -3.7% | 16,210 | 16,832 |
| Lawrence County | 85 | -3.71% | 14,716 | 15,283 |
| Marion County | 86 | -3.78% | 36,234 | 37,657 |
| Stephenson County | 87 | -3.91% | 42,829 | 44,573 |
| Hardin County | 88 | -3.98% | 3,501 | 3,646 |
| Perry County | 89 | -4.05% | 20,045 | 20,892 |
| Hancock County | 90 | -4.2% | 16,821 | 17,558 |
| Edwards County | 91 | -4.22% | 5,947 | 6,209 |
| Mason County | 92 | -4.25% | 12,498 | 13,053 |
| Clay County | 93 | -4.34% | 12,697 | 13,273 |
| Massac County | 94 | -4.48% | 13,503 | 14,137 |
| Vermilion County | 95 | -4.53% | 70,661 | 74,010 |
| Saline County | 96 | -4.54% | 22,664 | 23,741 |
| Henderson County | 97 | -5.43% | 5,991 | 6,335 |
| Gallatin County | 98 | -5.52% | 4,672 | 4,945 |
| Calhoun County | 99 | -5.63% | 4,155 | 4,403 |
| Greene County | 100 | -5.64% | 11,262 | 11,935 |
| Pulaski County | 101 | -7.3% | 4,801 | 5,179 |
| Alexander County | 102 | -13.67% | 4,465 | 5,172 |
Illinois's counties show varied growth patterns from 2020 to 2025. Kendall County leads with 10.4% annualized growth, followed by Champaign County (4.21%) and Grundy County (2.95%). The largest counties are Cook County (5,222,712), DuPage County (945,104), and Lake County (723,001). Of the 102 counties in Illinois, 20 are growing while 82 have experienced population decline. Overall, counties averaged -1.84% annualized growth, with total population growing by -0.16% annually.
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