What are the fastest-growing counties in Illinois?
Kendall County is the fastest-growing county in Illinois: its population grew 1.91% a year from 2020 to 2025, to 145,470 residents (Census PEP Vintage 2025). Grundy County (0.57%) and McHenry County (0.50%) follow. Illinois as a whole grew -0.12% a year to 12,719,141 residents.
Data as of 2026-09-23. Population, growth and migration: PEP Vintage 2025 · 2020–2025. Income migration: IRS SOI 2022–2023 (2-yr lag).
Top 10 counties in Illinois by population growth, 2020 to 2025
| Rank | County | Population | Growth (% per year) | Net domestic migration | Net international migration | IRS net AGI migration |
|---|---|---|---|---|---|---|
| 1 | Kendall County | 145,470 | 1.91% | +7,695 | +1,655 | +$32.6M |
| 2 | Grundy County | 54,052 | 0.57% | +1,238 | +259 | -$4.6M |
| 3 | McHenry County | 317,751 | 0.50% | +3,769 | +1,655 | -$22.4M |
| 4 | Will County | 712,253 | 0.44% | -3,587 | +10,594 | -$99.3M |
| 5 | Champaign County | 209,972 | 0.36% | -11,123 | +12,358 | -$156.0M |
| 6 | Kane County | 525,757 | 0.36% | -9,268 | +9,950 | -$103.6M |
| 7 | DeKalb County | 101,835 | 0.29% | -836 | +1,401 | -$1.7M |
| 8 | Lake County | 719,339 | 0.17% | -18,859 | +17,343 | -$144.5M |
| 9 | Bond County | 16,959 | 0.12% | +342 | +32 | -$0.6M |
| 10 | Clinton County | 37,128 | 0.12% | -17 | +195 | -$8.5M |
Where are people moving in Illinois?
Kendall County gained the most people from elsewhere in the United States: net domestic migration of +7,695 from 2020 to 2025 (Census PEP Vintage 2025). The table ranks every Illinois place with 10,000 or more residents by that figure; the IRS column shows net adjusted gross income migration for 2022 to 2023.
| Rank | County | Population | Growth (% per year) | Net domestic migration | Net international migration | IRS net AGI migration |
|---|---|---|---|---|---|---|
| 1 | Kendall County | 145,470 | 1.91% | +7,695 | +1,655 | +$32.6M |
| 2 | McHenry County | 317,751 | 0.50% | +3,769 | +1,655 | -$22.4M |
| 3 | Grundy County | 54,052 | 0.57% | +1,238 | +259 | -$4.6M |
| 4 | Williamson County | 67,225 | 0.03% | +854 | +213 | -$10.5M |
| 5 | Montgomery County | 28,076 | -0.12% | +487 | +11 | -$3.3M |
| 6 | Fulton County | 32,901 | -0.40% | +438 | +22 | -$8.7M |
| 7 | Tazewell County | 130,049 | -0.19% | +369 | +170 | -$9.7M |
| 8 | Monroe County | 34,840 | -0.07% | +368 | -6 | +$3.2M |
| 9 | Bond County | 16,959 | 0.12% | +342 | +32 | -$0.6M |
| 10 | Johnson County | 13,363 | 0.07% | +278 | +27 | +$0.3M |
Go past the headline numbers
The interactive Demographics map layer and the full report for a single place are part of paid plans.
Get the Demographics Report for Kendall CountyFrequently asked questions
- What are the fastest-growing counties in Illinois?
- By population growth from 2020 to 2025, the fastest are Kendall County (1.91% a year), Grundy County (0.57% a year), McHenry County (0.50% a year), Will County (0.44% a year) and Champaign County (0.36% a year) (Census PEP Vintage 2025). Only places with 10,000 or more residents are ranked.
- Where are people moving in Illinois?
- By net domestic migration from 2020 to 2025, the largest gains are Kendall County (+7,695), McHenry County (+3,769) and Grundy County (+1,238) (Census PEP Vintage 2025).
- How fast is Illinois growing overall?
- Illinois grew -0.12% a year from 2020 to 2025, to 12,719,141 residents, with net migration of -117,965 people (Census PEP Vintage 2025).
- Where does this Illinois data come from, and how current is it?
- Population, growth and migration come from the U.S. Census Bureau Population Estimates Program (PEP Vintage 2025 · 2020–2025). Income migration comes from IRS Statistics of Income (IRS SOI 2022–2023 (2-yr lag)). Counties with fewer than 10,000 residents are not ranked (15 of 102 in Illinois). Data last loaded 2026-09-23.
Data as of 2026-09-23: sources and periods
- Population, growth and migration
- U.S. Census Bureau, Population Estimates Program: PEP Vintage 2025 · 2020–2025. census.gov/programs-surveys/popest
- Income migration (net AGI)
- Internal Revenue Service, Statistics of Income migration data: IRS SOI 2022–2023 (2-yr lag). irs.gov/statistics/soi-tax-stats-migration-data
How to read the table
- Population is the Census July 1 estimate of the latest vintage.
- Growth is the compound annual rate over 2020 to 2025.
- Net domestic and international migration are cumulative people over 2020 to 2025.
- IRS net AGI migration is adjusted gross income that moved in, less what moved out, for 2022 to 2023. A plus sign means a net inflow.
- Places with fewer than 10,000 residents are left out of the rankings.