| Parish | Population | Area (km2) |
|---|---|---|
| Cook County | 5,240,700 | 2,525 |
| DuPage County | 932,126 | 876 |
| Lake County | 703,019 | 1,247 |
| Will County | 682,829 | 2,205 |
| Kane County | 523,643 | 1,361 |
| McHenry County | 307,409 | 1,583 |
| Winnebago County | 290,666 | 1,340 |
| Madison County | 267,225 | 1,914 |
| Saint Clair County | 264,052 | 1,742 |
| Champaign County | 204,897 | 2,587 |
| Sangamon County | 199,145 | 2,267 |
| Peoria County | 188,429 | 1,638 |
| McLean County | 174,647 | 3,075 |
| Rock Island County | 147,258 | 1,161 |
| Tazewell County | 136,352 | 1,698 |
| Kendall County | 119,348 | 835 |
| LaSalle County | 112,183 | 2,978 |
| Kankakee County | 112,120 | 1,767 |
| Macon County | 109,278 | 1,524 |
| DeKalb County | 104,741 | 1,635 |
| Vermilion County | 80,329 | 2,334 |
| Adams County | 67,130 | 2,257 |
| Williamson County | 66,924 | 1,154 |
| Jackson County | 59,814 | 1,558 |
| Whiteside County | 57,557 | 1,805 |
| Boone County | 53,957 | 728 |
| Coles County | 53,697 | 1,330 |
| Ogle County | 52,385 | 1,983 |
| Knox County | 52,078 | 1,866 |
| Grundy County | 50,228 | 1,113 |
| Henry County | 49,860 | 2,149 |
| Macoupin County | 46,880 | 2,253 |
| Stephenson County | 46,740 | 1,459 |
| Woodford County | 39,273 | 1,403 |
| Franklin County | 39,202 | 1,124 |
| Jefferson County | 38,644 | 1,506 |
| Marion County | 38,622 | 1,488 |
| Livingston County | 38,186 | 2,719 |
| Clinton County | 37,907 | 1,295 |
| Fulton County | 36,346 | 2,288 |
| Morgan County | 35,067 | 1,490 |
| Lee County | 34,858 | 1,886 |
| Effingham County | 34,307 | 1,249 |
| Christian County | 34,298 | 1,860 |
| Bureau County | 34,056 | 2,268 |
| Monroe County | 33,493 | 1,029 |
| Randolph County | 32,890 | 1,541 |
| McDonough County | 32,464 | 1,522 |
| Logan County | 29,964 | 1,606 |
| Montgomery County | 29,654 | 1,830 |
| Iroquois County | 28,982 | 2,898 |
| Saline County | 24,939 | 999 |
| Jersey County | 22,641 | 975 |
| Jo Daviess County | 22,407 | 1,603 |
| Shelby County | 22,119 | 1,988 |
| Fayette County | 22,060 | 1,875 |
| Perry County | 21,887 | 1,155 |
| Douglas County | 19,887 | 1,079 |
| Crawford County | 19,505 | 1,161 |
| Hancock County | 18,618 | 2,110 |
| Edgar County | 17,960 | 1,617 |
| Warren County | 17,726 | 1,403 |
| Union County | 17,583 | 1,098 |
| Bond County | 17,470 | 991 |
| Wayne County | 16,612 | 1,862 |
| Lawrence County | 16,558 | 967 |
| Piatt County | 16,433 | 1,145 |
| De Witt County | 16,420 | 1,047 |
| Clark County | 16,182 | 1,308 |
| Richland County | 16,182 | 942 |
| Mercer County | 16,178 | 1,472 |
| Pike County | 16,150 | 2,197 |
| Massac County | 15,073 | 628 |
| Carroll County | 14,910 | 1,207 |
| Moultrie County | 14,876 | 888 |
| White County | 14,549 | 1,298 |
| Washington County | 14,448 | 1,468 |
| Mason County | 14,248 | 1,457 |
| Ford County | 13,832 | 1,254 |
| Greene County | 13,629 | 1,410 |
| Clay County | 13,566 | 1,212 |
| Cass County | 13,324 | 1,001 |
| Johnson County | 12,677 | 907 |
| Menard County | 12,607 | 817 |
| Marshall County | 12,153 | 1,036 |
| Wabash County | 11,665 | 592 |
| Cumberland County | 10,939 | 898 |
| Jasper County | 9,592 | 1,291 |
| Hamilton County | 8,368 | 1,124 |
| Alexander County | 7,629 | 656 |
| Schuyler County | 7,444 | 1,139 |
| Henderson County | 6,990 | 1,029 |
| Brown County | 6,860 | 799 |
| Edwards County | 6,672 | 572 |
| Pulaski County | 5,908 | 532 |
| Stark County | 5,907 | 748 |
| Putnam County | 5,801 | 442 |
| Gallatin County | 5,415 | 847 |
| Scott County | 5,222 | 653 |
| Calhoun County | 5,059 | 734 |
| Pope County | 4,312 | 978 |
| Hardin County | 4,181 | 481 |
© 2018 AtlasBig.com