All counties in Illinois
| County Name | Population | State | Rank |
|---|
| Cook County | 5,194,675 | Illinois | 1 |
| Dupage County | 916,924 | Illinois | 2 |
| Lake County | 703,462 | Illinois | 3 |
| Will County | 677,560 | Illinois | 4 |
| Kane County | 515,269 | Illinois | 5 |
| Mchenry County | 308,760 | Illinois | 6 |
| Winnebago County | 295,266 | Illinois | 7 |
| St. Clair County | 270,056 | Illinois | 8 |
| Madison County | 269,282 | Illinois | 9 |
| Champaign County | 201,081 | Illinois | 10 |
| Sangamon County | 197,465 | Illinois | 11 |
| Peoria County | 186,494 | Illinois | 12 |
| Mclean County | 169,572 | Illinois | 13 |
| Rock Island County | 147,546 | Illinois | 14 |
| Tazewell County | 135,394 | Illinois | 15 |
| Kendall County | 114,736 | Illinois | 16 |
| Lasalle County | 113,924 | Illinois | 17 |
| Kankakee County | 113,449 | Illinois | 18 |
| Macon County | 110,768 | Illinois | 19 |
| Dekalb County | 105,160 | Illinois | 20 |
| Vermilion County | 81,625 | Illinois | 21 |
| Adams County | 67,103 | Illinois | 22 |
| Williamson County | 66,357 | Illinois | 23 |
| Jackson County | 60,218 | Illinois | 24 |
| Whiteside County | 58,498 | Illinois | 25 |
| Boone County | 54,165 | Illinois | 26 |
| Coles County | 53,873 | Illinois | 27 |
| Ogle County | 53,497 | Illinois | 28 |
| Knox County | 52,919 | Illinois | 29 |
| Henry County | 50,486 | Illinois | 30 |
| Grundy County | 50,063 | Illinois | 31 |
| Macoupin County | 47,765 | Illinois | 32 |
| Stephenson County | 47,711 | Illinois | 33 |
| Franklin County | 39,561 | Illinois | 34 |
| Marion County | 39,437 | Illinois | 35 |
| Livingston County | 38,950 | Illinois | 36 |
| Jefferson County | 38,827 | Illinois | 37 |
| Woodford County | 38,664 | Illinois | 38 |
| Clinton County | 37,762 | Illinois | 39 |
| Fulton County | 37,069 | Illinois | 40 |
| Lee County | 36,031 | Illinois | 41 |
| Morgan County | 35,547 | Illinois | 42 |
| Bureau County | 34,978 | Illinois | 43 |
| Christian County | 34,800 | Illinois | 44 |
| Effingham County | 34,242 | Illinois | 45 |
| Randolph County | 33,476 | Illinois | 46 |
| Monroe County | 32,957 | Illinois | 47 |
| Mcdonough County | 32,612 | Illinois | 48 |
| Logan County | 30,305 | Illinois | 49 |
| Montgomery County | 30,104 | Illinois | 50 |
| Iroquois County | 29,718 | Illinois | 51 |
| Saline County | 24,913 | Illinois | 52 |
| Jersey County | 22,985 | Illinois | 53 |
| Jo Daviess County | 22,678 | Illinois | 54 |
| Shelby County | 22,363 | Illinois | 55 |
| Perry County | 22,350 | Illinois | 56 |
| Fayette County | 22,140 | Illinois | 57 |
| Douglas County | 19,980 | Illinois | 58 |
| Crawford County | 19,817 | Illinois | 59 |
| Hancock County | 19,104 | Illinois | 60 |
| Edgar County | 18,576 | Illinois | 61 |
| Union County | 17,808 | Illinois | 62 |
| Bond County | 17,768 | Illinois | 63 |
| Warren County | 17,707 | Illinois | 64 |
| Lawrence County | 16,833 | Illinois | 65 |
| Wayne County | 16,760 | Illinois | 66 |
| Piatt County | 16,729 | Illinois | 67 |
| De Witt County | 16,561 | Illinois | 68 |
| Mercer County | 16,434 | Illinois | 69 |
| Pike County | 16,430 | Illinois | 70 |
| Clark County | 16,335 | Illinois | 71 |
| Richland County | 16,233 | Illinois | 72 |
| Massac County | 15,429 | Illinois | 73 |
| Carroll County | 15,387 | Illinois | 74 |
| Moultrie County | 14,846 | Illinois | 75 |
| Washington County | 14,716 | Illinois | 76 |
| Mason County | 14,666 | Illinois | 77 |
| White County | 14,665 | Illinois | 78 |
| Ford County | 14,081 | Illinois | 79 |
| Greene County | 13,886 | Illinois | 80 |
| Clay County | 13,815 | Illinois | 81 |
| Cass County | 13,642 | Illinois | 82 |
| Menard County | 12,705 | Illinois | 83 |
| Marshall County | 12,640 | Illinois | 84 |
| Johnson County | 12,582 | Illinois | 85 |
| Wabash County | 11,947 | Illinois | 86 |
| Cumberland County | 11,048 | Illinois | 87 |
| Jasper County | 9,698 | Illinois | 88 |
| Hamilton County | 8,457 | Illinois | 89 |
| Alexander County | 8,238 | Illinois | 90 |
| Schuyler County | 7,544 | Illinois | 91 |
| Henderson County | 7,331 | Illinois | 92 |
| Brown County | 6,937 | Illinois | 93 |
| Edwards County | 6,721 | Illinois | 94 |
| Pulaski County | 6,161 | Illinois | 95 |
| Putnam County | 6,006 | Illinois | 96 |
| Stark County | 5,994 | Illinois | 97 |
| Gallatin County | 5,589 | Illinois | 98 |
| Scott County | 5,355 | Illinois | 99 |
| Calhoun County | 5,089 | Illinois | 100 |
| Pope County | 4,470 | Illinois | 101 |
| Hardin County | 4,320 | Illinois | 102 |