Illinois Counties by Population (2026)
2026 Pop.
500K
1M
1.5M
2M
2.5M
3M
3.5M
4M
4.5M
5M
Top 5 Most Populous Counties
5,262,807
953,066
727,398
718,983
528,509
102 Counties
| County | 2026 Pop. ↓ | Area (mi²) | Density | Change (2020) |
|---|---|---|---|---|
| Cook County | 5,262,807 | 945 | 5,569 | -0.08% |
| DuPage County | 953,066 | 328 | 2,906 | 2.31% |
| Lake County | 727,398 | 444 | 1,638 | 1.96% |
| Will County | 718,983 | 836 | 860 | 3.17% |
| Kane County | 528,509 | 519 | 1,018 | 2.34% |
| McHenry County | 321,007 | 603 | 532 | 3.56% |
| Winnebago County | 286,942 | 513 | 559 | 0.69% |
| Madison County | 262,167 | 716 | 366 | -1.35% |
| St. Clair County | 249,259 | 658 | 379 | -3.04% |
| Champaign County | 217,496 | 1K | 218 | 5.45% |
| Sangamon County | 194,603 | 868 | 224 | -0.83% |
| Peoria County | 181,420 | 619 | 293 | -0.05% |
| McLean County | 173,221 | 1.2K | 146 | 1.16% |
| Kendall County | 149,055 | 320 | 466 | 12.62% |
| Rock Island County | 144,315 | 427 | 338 | -0.03% |
| Tazewell County | 129,793 | 646 | 201 | -1.14% |
| LaSalle County | 108,376 | 1.1K | 95 | -0.94% |
| Kankakee County | 106,458 | 676 | 157 | -0.88% |
| DeKalb County | 102,683 | 631 | 163 | 2.31% |
| Macon County | 100,703 | 581 | 173 | -2.95% |
| Vermilion County | 70,216 | 898 | 78 | -5.13% |
| Williamson County | 67,718 | 420 | 161 | 0.89% |
| Adams County | 63,457 | 855 | 74 | -3.3% |
| Whiteside County | 54,807 | 684 | 80 | -1.38% |
| Grundy County | 54,331 | 418 | 130 | 3.42% |
| Jackson County | 53,863 | 584 | 92 | 1.12% |
| Boone County | 53,461 | 281 | 190 | 0.23% |
| Ogle County | 51,253 | 759 | 68 | -0.98% |
| Knox County | 48,822 | 716 | 68 | -1.98% |
| Henry County | 47,807 | 823 | 58 | -2.79% |
| Coles County | 46,205 | 508 | 91 | -1.87% |
| Macoupin County | 43,431 | 863 | 50 | -3.32% |
| Stephenson County | 42,570 | 564 | 75 | -4.49% |
| Woodford County | 38,096 | 528 | 72 | -0.81% |
| Clinton County | 37,489 | 474 | 79 | 1.56% |
| Franklin County | 36,787 | 409 | 90 | -2.47% |
| Marion County | 36,031 | 573 | 63 | -4.32% |
| Jefferson County | 35,659 | 571 | 62 | -3.62% |
| Livingston County | 35,483 | 1K | 34 | -0.93% |
| Effingham County | 34,900 | 479 | 73 | 0.56% |
| Monroe County | 34,619 | 385 | 90 | -0.96% |
| Lee County | 33,420 | 725 | 46 | -1.89% |
| Christian County | 33,103 | 709 | 47 | -2.59% |
| Morgan County | 32,308 | 569 | 57 | -3.54% |
| Fulton County | 32,202 | 866 | 37 | -4.03% |
| Bureau County | 31,942 | 869 | 37 | -3.86% |
| Randolph County | 29,723 | 575 | 52 | -1.2% |
| Logan County | 27,538 | 618 | 45 | -1.32% |
| Montgomery County | 27,333 | 704 | 39 | -3.22% |
| Iroquois County | 26,135 | 1.1K | 23 | -3.08% |
| McDonough County | 26,082 | 589 | 44 | -3.81% |
| Saline County | 22,502 | 380 | 59 | -5.22% |
| Jersey County | 21,134 | 370 | 57 | -1.67% |
| Jo Daviess County | 21,086 | 601 | 35 | -4.58% |
| Fayette County | 21,053 | 716 | 29 | -2.01% |
| Shelby County | 20,440 | 759 | 27 | -2.23% |
| Douglas County | 20,006 | 417 | 48 | 1.14% |
| Perry County | 19,818 | 442 | 45 | -5.14% |
| Crawford County | 18,480 | 444 | 42 | -0.84% |
| Union County | 16,926 | 413 | 41 | -2.15% |
| Hancock County | 16,634 | 794 | 21 | -5.26% |
| Bond County | 16,454 | 380 | 43 | -2.38% |
| Piatt County | 16,444 | 439 | 37 | -1.43% |
| Edgar County | 16,310 | 623 | 26 | -2.96% |
| Warren County | 16,203 | 542 | 30 | -3.74% |
| Wayne County | 16,034 | 714 | 22 | -0.79% |
| Carroll County | 15,348 | 445 | 34 | -2.1% |
| De Witt County | 15,295 | 398 | 38 | -1.09% |
| Richland County | 15,082 | 360 | 42 | -4.57% |
| Mercer County | 14,964 | 561 | 27 | -4.27% |
| Clark County | 14,792 | 501 | 30 | -4.25% |
| Lawrence County | 14,631 | 372 | 39 | -4.27% |
| Moultrie County | 14,441 | 336 | 43 | -0.35% |
| Pike County | 14,096 | 831 | 17 | -3.7% |
| Ford County | 13,721 | 486 | 28 | 1.55% |
| Washington County | 13,465 | 563 | 24 | -1.94% |
| Massac County | 13,379 | 237 | 56 | -5.36% |
| Johnson County | 13,250 | 344 | 39 | -0.54% |
| White County | 13,221 | 495 | 27 | -4.29% |
| Cass County | 12,581 | 376 | 33 | -3.04% |
| Clay County | 12,573 | 468 | 27 | -5.27% |
| Mason County | 12,453 | 539 | 23 | -4.6% |
| Menard County | 11,897 | 314 | 38 | -3.06% |
| Marshall County | 11,356 | 387 | 29 | -3.02% |
| Greene County | 11,107 | 543 | 20 | -6.94% |
| Wabash County | 10,873 | 223 | 49 | -3.91% |
| Cumberland County | 10,371 | 346 | 30 | -0.63% |
| Jasper County | 8,964 | 495 | 18 | -3.14% |
| Hamilton County | 7,682 | 435 | 18 | -3.89% |
| Schuyler County | 6,800 | 437 | 16 | -1.02% |
| Brown County | 6,319 | 306 | 21 | 1.31% |
| Henderson County | 5,934 | 379 | 16 | -6.33% |
| Edwards County | 5,910 | 222 | 27 | -4.82% |
| Putnam County | 5,723 | 160 | 36 | 1.63% |
| Stark County | 5,282 | 288 | 18 | -1.97% |
| Scott County | 4,940 | 251 | 20 | -2.64% |
| Pulaski County | 4,723 | 199 | 24 | -8.8% |
| Gallatin County | 4,654 | 323 | 14 | -5.88% |
| Alexander County | 4,336 | 235 | 18 | -16.16% |
| Calhoun County | 4,086 | 254 | 16 | -7.2% |
| Pope County | 3,679 | 369 | 10 | -2.1% |
| Hardin County | 3,452 | 177 | 20 | -5.32% |
Overview of Illinois Counties
There are 102 counties in Illinois.
Cook County is the largest county in the state, with a population of 5,262,807. The most recent census shows that its population has decreased by 0.00% since the previous census.
A number of other Illinois counties also boast relatively large populations for their state, though not able to match the density of Cook County:
- DuPage County : 953,066
- Lake County : 727,398
Illinois Counties with the Fewest Residents
The smallest county in Illinois is Hardin County , with a population of just 3,452. This total represents a decrease of 0.1% since the last census count was performed.
Other small counties include:
- Pope County : 3,679
- Calhoun County : 4,086
- Alexander County : 4,336
Illinois Counties with Rapid Growth
Kendall County , with its sizeable population of 149,055, has shown the largest population growth, with an increase of 0.1% since the last census.
Will County has also had relatively high population growth of 0.03% with 718,983 residents.
On the other hand, Alexander County has had the largest decrease in population, with its 4,336 current residents totalling 0.2% less than the previous census.
Sources
- US Census State Population Estimates - Most recent state estimates from the Census Bureau's Population Estimates Program
- US Census County Population Estimates - Most recent county estimates from the Census Bureau's Population Estimates Program
- American Community Survey (2009 - 2013)
- Census QuickFacts
- Historical Populations of States and Counties (1790 - 1990)