Illinois Population By County in 2015
Updated on June 16, 2025.
Based on the US Census Vintage data estimates, in 2015, the population of Illinois was 12,859,585. Among all Illinois counties, Cook had the highest population (5,243,371), followed by DuPage (933,669), and Lake (704,687). Hardin was the least populated county (4,065).
Hover over or click on the counties in the map below to see the populations. The data can also be found in a table below. You can use the table to sort, filter, and explore the data further.
You can see similar information for other states and by state for the United States.
Related Topics: Illinois Census Vintage Data Topic List.
Data Source: US Census Bureau (Vintage).
See this for other years:
Illinois Population By County in 2015
Illinois Population By County in 2015
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| County | Population | % of State Population |
|---|---|---|
| Adams | 66850 | 0.52 |
| Alexander | 6763 | 0.05 |
| Bond | 16688 | 0.13 |
| Boone | 53571 | 0.42 |
| Brown | 6755 | 0.05 |
| Bureau | 33494 | 0.26 |
| Calhoun | 4858 | 0.04 |
| Carroll | 14638 | 0.11 |
| Cass | 12843 | 0.10 |
| Champaign | 209534 | 1.63 |
| Christian | 33480 | 0.26 |
| Clark | 15881 | 0.12 |
| Clay | 13395 | 0.10 |
| Clinton | 37657 | 0.29 |
| Coles | 52217 | 0.41 |
| Cook | 5243371 | 40.77 |
| Crawford | 19262 | 0.15 |
| Cumberland | 10869 | 0.09 |
| DeKalb | 104238 | 0.81 |
| De Witt | 16185 | 0.13 |
| Douglas | 19827 | 0.15 |
| DuPage | 933669 | 7.26 |
| Edgar | 17625 | 0.14 |
| Edwards | 6514 | 0.05 |
| Effingham | 34200 | 0.27 |
| Fayette | 22048 | 0.17 |
| Ford | 13527 | 0.11 |
| Franklin | 39398 | 0.31 |
| Fulton | 35709 | 0.28 |
| Gallatin | 5224 | 0.04 |
| Greene | 13345 | 0.10 |
| Grundy | 50358 | 0.39 |
| Hamilton | 8247 | 0.06 |
| Hancock | 18217 | 0.14 |
| Hardin | 4065 | 0.03 |
| Henderson | 7001 | 0.05 |
| Henry | 49654 | 0.39 |
| Iroquois | 28529 | 0.22 |
| Jackson | 59249 | 0.46 |
| Jasper | 9630 | 0.08 |
| Jefferson | 38290 | 0.30 |
| Jersey | 22268 | 0.17 |
| Jo Daviess | 22068 | 0.17 |
| Johnson | 12768 | 0.10 |
| Kane | 528562 | 4.11 |
| Kankakee | 111786 | 0.87 |
| Kendall | 122892 | 0.96 |
| Knox | 51377 | 0.40 |
| Lake | 704687 | 5.48 |
| LaSalle | 111015 | 0.86 |
| Lawrence | 16467 | 0.13 |
| Lee | 34521 | 0.27 |
| Livingston | 36615 | 0.28 |
| Logan | 29286 | 0.23 |
| McDonough | 31461 | 0.25 |
| McHenry | 307595 | 2.39 |
| McLean | 173222 | 1.35 |
| Macon | 107398 | 0.84 |
| Macoupin | 45887 | 0.36 |
| Madison | 266112 | 2.07 |
| Marion | 38381 | 0.30 |
| Marshall | 11925 | 0.09 |
| Mason | 13862 | 0.11 |
| Massac | 14568 | 0.11 |
| Menard | 12364 | 0.10 |
| Mercer | 15748 | 0.12 |
| Monroe | 33811 | 0.26 |
| Montgomery | 29196 | 0.23 |
| Morgan | 34693 | 0.27 |
| Moultrie | 14747 | 0.12 |
| Ogle | 51572 | 0.40 |
| Peoria | 186552 | 1.45 |
| Perry | 21522 | 0.17 |
| Piatt | 16356 | 0.13 |
| Pike | 15794 | 0.12 |
| Pope | 4302 | 0.03 |
| Pulaski | 5662 | 0.04 |
| Putnam | 5729 | 0.05 |
| Randolph | 32754 | 0.26 |
| Richland | 15952 | 0.12 |
| Rock Island | 146161 | 1.14 |
| St. Clair | 265008 | 2.06 |
| Saline | 24495 | 0.19 |
| Sangamon | 198973 | 1.55 |
| Schuyler | 7150 | 0.06 |
| Scott | 5112 | 0.04 |
| Shelby | 21819 | 0.17 |
| Stark | 5508 | 0.04 |
| Stephenson | 45680 | 0.36 |
| Tazewell | 134350 | 1.05 |
| Union | 17285 | 0.13 |
| Vermilion | 79209 | 0.62 |
| Wabash | 11627 | 0.09 |
| Warren | 17448 | 0.14 |
| Washington | 14259 | 0.11 |
| Wayne | 16534 | 0.13 |
| White | 14204 | 0.11 |
| Whiteside | 56943 | 0.44 |
| Will | 685825 | 5.33 |
| Williamson | 67457 | 0.53 |
| Winnebago | 287237 | 2.23 |
| Woodford | 38949 | 0.30 |