Illinois — All 101 Counties
Illinois has 101 counties with 1,460 communities and a combined population of 11,221,014.
| County | Towns | Population |
| Cook County | 136 | 5,495,088 |
| DuPage County | 27 | 963,858 |
| Lake County | 55 | 617,291 |
| Kendall County | 11 | 276,681 |
| Kane County | 21 | 250,747 |
| Madison County | 33 | 222,693 |
| Will County | 34 | 211,214 |
| McHenry County | 35 | 197,676 |
| St. Clair County | 30 | 196,391 |
| Peoria County | 21 | 181,644 |
| Champaign County | 28 | 178,635 |
| Ogle County | 18 | 170,233 |
| Sangamon County | 26 | 163,927 |
| McLean County | 24 | 156,764 |
| Rock Island County | 22 | 124,785 |
| Macon County | 14 | 90,896 |
| DeKalb County | 13 | 87,397 |
| Kankakee County | 19 | 79,243 |
| Tazewell County | 17 | 76,567 |
| LaSalle County | 28 | 73,098 |
| Grundy County | 17 | 67,405 |
| Boone County | 10 | 64,583 |
| Winnebago County | 9 | 58,817 |
| Vermilion County | 21 | 50,157 |
| Adams County | 25 | 47,790 |
| Williamson County | 16 | 45,612 |
| Knox County | 16 | 41,954 |
| Henry County | 18 | 38,492 |
| Whiteside County | 13 | 37,009 |
| Bureau County | 25 | 36,480 |
| Coles County | 8 | 35,956 |
| Clinton County | 15 | 35,269 |
| Jackson County | 12 | 34,781 |
| Stephenson County | 13 | 34,341 |
| Lee County | 14 | 31,224 |
| Monroe County | 7 | 27,808 |
| Macoupin County | 25 | 27,431 |
| Christian County | 16 | 26,569 |
| Morgan County | 12 | 26,143 |
| Franklin County | 17 | 24,945 |
| McDonough County | 12 | 24,640 |
| Fulton County | 20 | 24,188 |
| Crawford County | 17 | 21,663 |
| Randolph County | 14 | 21,291 |
| Montgomery County | 17 | 21,013 |
| Livingston County | 13 | 20,996 |
| Logan County | 14 | 19,997 |
| Effingham County | 9 | 19,596 |
| Jefferson County | 10 | 19,542 |
| Woodford County | 13 | 19,234 |
| Iroquois County | 21 | 17,818 |
| Saline County | 7 | 15,711 |
| Douglas County | 9 | 14,631 |
| Marion County | 12 | 13,534 |
| Jo Daviess County | 12 | 12,881 |
| Hancock County | 16 | 12,383 |
| Perry County | 6 | 12,299 |
| Jersey County | 8 | 12,045 |
| Piatt County | 9 | 11,923 |
| Edgar County | 8 | 11,626 |
| Warren County | 5 | 11,133 |
| Bond County | 10 | 10,905 |
| De Witt County | 8 | 10,811 |
| Carroll County | 8 | 10,713 |
| Pike County | 19 | 10,441 |
| Mercer County | 18 | 10,379 |
| Richland County | 6 | 10,357 |
| Fayette County | 8 | 10,123 |
| Cass County | 5 | 9,401 |
| Lawrence County | 5 | 8,936 |
| Greene County | 9 | 8,486 |
| Shelby County | 10 | 8,286 |
| Union County | 6 | 8,186 |
| Mason County | 9 | 8,095 |
| White County | 8 | 8,074 |
| Clark County | 5 | 8,039 |
| Marshall County | 8 | 8,029 |
| Wabash County | 4 | 7,759 |
| Moultrie County | 7 | 7,708 |
| Clay County | 6 | 7,383 |
| Washington County | 12 | 7,311 |
| Menard County | 6 | 7,296 |
| Wayne County | 10 | 7,214 |
| Massac County | 3 | 6,842 |
| Edwards County | 5 | 4,764 |
| Cumberland County | 5 | 4,707 |
| Johnson County | 7 | 4,168 |
| Stark County | 4 | 3,843 |
| Alexander County | 7 | 3,725 |
| Jasper County | 8 | 3,693 |
| Hamilton County | 4 | 3,641 |
| Henderson County | 9 | 3,530 |
| Putnam County | 6 | 3,499 |
| Gallatin County | 7 | 3,453 |
| Pulaski County | 7 | 3,282 |
| Scott County | 10 | 2,975 |
| Schuyler County | 4 | 2,915 |
| Brown County | 4 | 2,540 |
| Calhoun County | 5 | 1,511 |
| Hardin County | 3 | 1,453 |
| Pope County | 2 | 803 |