County facts · Population growth · October 24, 2026
Fastest Growing Counties in Illinois, 2020 to 2025
Illinois's fastest growing counties by percent and by people added, April 2020 to July 2025 Census estimates, with each official parcel map.
Looking for the fastest growing counties in Illinois? From the Census Bureau's April 1, 2020 estimates base to its July 1, 2025 estimate, Illinois went from about 12,821,741 to 12,719,141 residents, a change of −102,600 (−0.8%). The fastest growing county by percentage was Kendall County (+10.3%), while Will County added the most people (+14,892, +2.1%).
Every row below links to the county's Platbookmapper page and straight to its official parcel viewer, handy if growth is why you are looking at land there.
Illinois growth at a glance
- Counties: 102
- Statewide, April 2020 to July 2025: −102,600 residents (−0.8%); July 2024 to July 2025 alone: +16,108 (+0.1%)
- Grew: 18 of 102 · Lost residents: 84
- Fastest growing by percent: Kendall County (+10.3%); most people added: Will County (+14,892)
- Counties with more deaths than births over the period: 85 of 102
The 10 fastest growing Illinois counties by percent
| # | County | Apr 2020 | Jul 2025 | Change | % change | Parcel viewer |
|---|---|---|---|---|---|---|
| 1 | Kendall County | 131,876 | 145,470 | +13,594 | +10.3% | county web map |
| 2 | Grundy County | 52,559 | 54,052 | +1,493 | +2.8% | county web map |
| 3 | Brown County | 6,245 | 6,401 | +156 | +2.5% | myGISonline |
| 4 | McHenry County | 310,305 | 317,751 | +7,446 | +2.4% | county web map |
| 5 | Will County | 697,361 | 712,253 | +14,892 | +2.1% | county web map |
| 6 | Kane County | 516,709 | 525,757 | +9,048 | +1.8% | county web map |
| 7 | Champaign County | 206,445 | 209,972 | +3,527 | +1.7% | county web map |
| 8 | DeKalb County | 100,522 | 101,835 | +1,313 | +1.3% | county web map |
| 9 | Lake County | 714,394 | 719,339 | +4,945 | +0.7% | county web map |
| 10 | Douglas County | 19,746 | 19,880 | +134 | +0.7% | listed link under review |
These 10 added about 56,548 people combined. The median county changed by −2.3%.
The 10 counties that added the most people
| # | County | People added | % change | Jul 2025 | Parcel viewer |
|---|---|---|---|---|---|
| 1 | Will County | +14,892 | +2.1% | 712,253 | county web map |
| 2 | Kendall County | +13,594 | +10.3% | 145,470 | county web map |
| 3 | Kane County | +9,048 | +1.8% | 525,757 | county web map |
| 4 | McHenry County | +7,446 | +2.4% | 317,751 | county web map |
| 5 | Lake County | +4,945 | +0.7% | 719,339 | county web map |
| 6 | Champaign County | +3,527 | +1.7% | 209,972 | county web map |
| 7 | Grundy County | +1,493 | +2.8% | 54,052 | county web map |
| 8 | DeKalb County | +1,313 | +1.3% | 101,835 | county web map |
| 9 | DuPage County | +1,269 | +0.1% | 934,298 | county web map |
| 10 | Clinton County | +224 | +0.6% | 37,128 | ArcGIS |
The top 10 account for about 98% of all the gains in the counties that grew.
Where the new residents came from
The Census Bureau splits each change into natural change (births minus deaths), net domestic migration (moves from other parts of the US) and net international migration. Totals for April 2020 to July 2025 in the five fastest growing counties:
| County | Births minus deaths | Net domestic moves | Net international moves | Total change |
|---|---|---|---|---|
| Kendall County | +3,997 | +7,928 | +1,656 | +13,594 |
| Grundy County | +34 | +1,212 | +259 | +1,493 |
| Brown County | −33 | +207 | +1 | +156 |
| McHenry County | +2,313 | +3,368 | +1,656 | +7,446 |
| Will County | +7,968 | −4,229 | +10,598 | +14,892 |
In 4 of these 5, moves from elsewhere in the US were the biggest source of growth. The three parts do not add up exactly to the total because the Census Bureau also carries a small residual.
The last year alone: July 2024 to July 2025
- Bond County: +2.2% (+359)
- Kendall County: +1.6% (+2,345)
- DeKalb County: +1.2% (+1,214)
- Stark County: +0.9% (+50)
- Piatt County: +0.9% (+149)
2 of these 5 are also in the 2020–2025 top 10.
Counties losing residents
84 of Illinois's 102 counties had fewer residents in July 2025 than in April 2020. The steepest declines:
- Alexander County: −12.8% (−669, now about 4,570)
- Lawrence County: −9.9% (−1,511, now about 13,790)
- Pulaski County: −7.4% (−386, now about 4,820)
- Gallatin County: −6.6% (−326, now about 4,616)
- Henderson County: −6.4% (−408, now about 5,984)
What fast growth means on a parcel map
- New lots show up as plats first. When land is subdivided, the plat is recorded with the county and the parcel layer catches up on its own schedule, so a brand-new lot may not appear on the map for a while. Check the recorder's recent plats if a parcel looks missing.
- Parcel numbers change after splits. A tract that was one parcel last year can be several today. Search by owner name or address as well as by an old parcel number.
- City limits move. Growing cities annex land, which changes who handles zoning and permits even though the county still keeps the deed and the tax map.
- Percent is not the same as people. A small county can post a big percentage on a modest number of new residents, so read the people-added column too.
Related guides
- Largest counties in Illinois
- Illinois county GIS websites by viewer
- Illinois landowner maps for hunting
- Fastest growing counties in the US
- US counties losing population
More: All Illinois counties on Platbookmapper
Sources
- U.S. Census Bureau, Population Estimates Program, county totals, Vintage 2025 (April 1, 2020 estimates base and July 1, 2020–2025 estimates, with components of change). Percent change is from the April 1, 2020 estimates base to the July 1, 2025 estimate.
- Platbookmapper county GIS directory (live data file behind our county pages, pulled October 24, 2026) for each official parcel viewer.