The graph below ranks each Iowa County by total residents according to the 2006 census estimates.
Iowa total population by county
| County | Total Population |
| Polk |  408,888 |
| Linn | 201,853 |
| Scott | 162,621 |
| Black Hawk | 126,106 |
| Johnson | 118,038 |
| Woodbury | 102,972 |
| Dubuque | 92,384 |
| Pottawattamie | 90,218 |
| Story | 80,145 |
| Dallas | 54,525 |
| Clinton | 49,782 |
| Cerro Gordo | 44,384 |
| Warren | 43,926 |
| Muscatine | 42,883 |
| Des Moines | 40,885 |
| Marshall | 39,555 |
| Webster | 38,960 |
| Jasper | 37,409 |
| Lee | 36,338 |
| Wapello | 36,010 |
| Marion | 32,987 |
| Sioux | 32,525 |
| Benton | 26,962 |
| Boone | 26,584 |
| Plymouth | 24,906 |
| Bremer | 23,837 |
| Mahaska | 22,298 |
| Washington | 21,529 |
| Winneshiek | 21,263 |
| Buchanan | 21,045 |
| Fayette | 20,996 |
| Carroll | 20,963 |
| Jones | 20,505 |
| Henry | 20,405 |
| Jackson | 20,290 |
| Buena Vista | 20,091 |
| Poweshiek | 19,007 |
| Cedar | 18,326 |
| Clayton | 18,251 |
| Tama | 17,890 |
| Delaware | 17,848 |
| Hardin | 17,791 |
| Crawford | 16,948 |
| Dickinson | 16,924 |
| Clay | 16,801 |
| Floyd | 16,441 |
| Page | 16,263 |
| Iowa | 16,140 |
| Hamilton | 16,087 |
| Kossuth | 16,011 |
| Jefferson | 15,945 |
| Harrison | 15,745 |
| Mills | 15,595 |
| Madison | 15,547 |
| Butler | 15,073 |
| Allamakee | 14,796 |
| O'Brien | 14,409 |
| Cass | 14,124 |
| Appanoose | 13,422 |
| Wright | 13,419 |
| Shelby | 12,489 |
| Chickasaw | 12,412 |
| Grundy | 12,320 |
| Cherokee | 12,094 |
| Union | 12,093 |
| Louisa | 11,858 |
| Hancock | 11,680 |
| Lyon | 11,636 |
| Montgomery | 11,365 |
| Guthrie | 11,344 |
| Winnebago | 11,216 |
| Keokuk | 11,081 |
| Mitchell | 10,856 |
| Franklin | 10,708 |
| Sac | 10,682 |
| Emmet | 10,479 |
| Calhoun | 10,437 |
| Humboldt | 9,975 |
| Greene | 9,809 |
| Howard | 9,677 |
| Palo Alto | 9,549 |
| Lucas | 9,543 |
| Monona | 9,343 |
| Clarke | 9,156 |
| Decatur | 8,656 |
| Davis | 8,602 |
| Van Buren | 7,836 |
| Pocahontas | 7,794 |
| Fremont | 7,737 |
| Monroe | 7,725 |
| Adair | 7,714 |
| Worth | 7,698 |
| Ida | 7,180 |
| Osceola | 6,629 |
| Wayne | 6,542 |
| Taylor | 6,540 |
| Audubon | 6,278 |
| Ringgold | 5,289 |
| Adams | 4,192 |