The largest county in Iowa
There are two right answers. By land area it is Kossuth County; by population it is Polk County. Which one you want depends on what you meant by largest.
Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025. Retrieved 30 August 2026.
By land area
| Rank | Name | Land area | Population |
|---|---|---|---|
| 1 | Kossuth County | 972.7 sq mi | 14,322 |
| 2 | Pottawattamie County | 951.3 sq mi | 92,996 |
| 3 | Woodbury County | 872.9 sq mi | 106,649 |
| 4 | Plymouth County | 862.8 sq mi | 25,697 |
| 5 | Clayton County | 778.5 sq mi | 16,845 |
| 6 | Sioux County | 767.9 sq mi | 36,774 |
| 7 | Fayette County | 730.8 sq mi | 19,047 |
| 8 | Jasper County | 730.4 sq mi | 38,153 |
| 9 | Tama County | 721 sq mi | 16,796 |
| 10 | Linn County | 717 sq mi | 232,028 |
By population
| Rank | Name | Population | Density |
|---|---|---|---|
| 1 | Polk County | 516,546 | 902 per sq mi |
| 2 | Linn County | 232,028 | 324 per sq mi |
| 3 | Scott County | 175,259 | 383 per sq mi |
| 4 | Johnson County | 160,044 | 261 per sq mi |
| 5 | Black Hawk County | 131,532 | 232 per sq mi |
| 6 | Dallas County | 118,457 | 201 per sq mi |
| 7 | Woodbury County | 106,649 | 122 per sq mi |
| 8 | Story County | 101,291 | 177 per sq mi |
| 9 | Dubuque County | 99,381 | 163 per sq mi |
| 10 | Pottawattamie County | 92,996 | 97.8 per sq mi |
And the smallest
More on Iowa
Rebuilt from source data 30 August 2026. How these figures are produced.