What are the fastest-growing counties in Iowa?
Dallas County is the fastest-growing county in Iowa: its population grew 3.34% a year from 2020 to 2025, to 118,457 residents (Census PEP Vintage 2025). Warren County (1.74%) and Polk County (0.94%) follow. Iowa as a whole grew 0.29% a year to 3,238,387 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 Iowa by population growth, 2020 to 2025
| Rank | County | Population | Growth (% per year) | Net domestic migration | Net international migration | IRS net AGI migration |
|---|---|---|---|---|---|---|
| 1 | Dallas County | 118,457 | 3.34% | +12,064 | +2,077 | +$41.3M |
| 2 | Warren County | 57,331 | 1.74% | +4,181 | +121 | +$40.6M |
| 3 | Polk County | 516,546 | 0.94% | +1,974 | +11,325 | -$10.5M |
| 4 | Johnson County | 160,044 | 0.89% | -1,050 | +4,082 | -$69.0M |
| 5 | Madison County | 17,270 | 0.76% | +558 | +17 | -$0.6M |
| 6 | Lyon County | 12,354 | 0.71% | +163 | +95 | -$2.0M |
| 7 | Jones County | 21,253 | 0.57% | +713 | +22 | +$0.7M |
| 8 | Story County | 101,291 | 0.53% | -1,018 | +2,699 | -$50.3M |
| 9 | Mills County | 14,793 | 0.52% | +463 | +13 | +$3.4M |
| 10 | Sioux County | 36,774 | 0.49% | -904 | +720 | -$4.7M |
Where are people moving in Iowa?
Dallas County gained the most people from elsewhere in the United States: net domestic migration of +12,064 from 2020 to 2025 (Census PEP Vintage 2025). The table ranks every Iowa 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 | Dallas County | 118,457 | 3.34% | +12,064 | +2,077 | +$41.3M |
| 2 | Warren County | 57,331 | 1.74% | +4,181 | +121 | +$40.6M |
| 3 | Polk County | 516,546 | 0.94% | +1,974 | +11,325 | -$10.5M |
| 4 | Marion County | 34,192 | 0.46% | +919 | +93 | +$7.9M |
| 5 | Jones County | 21,253 | 0.57% | +713 | +22 | +$0.7M |
| 6 | Dickinson County | 18,077 | 0.34% | +615 | +52 | +$9.4M |
| 7 | Madison County | 17,270 | 0.76% | +558 | +17 | -$0.6M |
| 8 | Boone County | 26,799 | 0.07% | +489 | +6 | -$3.6M |
| 9 | Mills County | 14,793 | 0.52% | +463 | +13 | +$3.4M |
| 10 | Benton County | 26,004 | 0.35% | +397 | +29 | -$3.0M |
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 Dallas CountyFrequently asked questions
- What are the fastest-growing counties in Iowa?
- By population growth from 2020 to 2025, the fastest are Dallas County (3.34% a year), Warren County (1.74% a year), Polk County (0.94% a year), Johnson County (0.89% a year) and Madison County (0.76% a year) (Census PEP Vintage 2025). Only places with 10,000 or more residents are ranked.
- Where are people moving in Iowa?
- By net domestic migration from 2020 to 2025, the largest gains are Dallas County (+12,064), Warren County (+4,181) and Polk County (+1,974) (Census PEP Vintage 2025).
- How fast is Iowa growing overall?
- Iowa grew 0.29% a year from 2020 to 2025, to 3,238,387 residents, with net migration of +35,909 people (Census PEP Vintage 2025).
- Where does this Iowa 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 (27 of 99 in Iowa). 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.