| County | Rank | Change (2020) ↓ | 2025 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Dallas County | 1 | 16.36% | 116,984 | 100,536 |
| Warren County | 2 | 8.4% | 57,009 | 52,591 |
| Lyon County | 3 | 5.77% | 12,618 | 11,930 |
| Polk County | 4 | 4.13% | 513,397 | 493,022 |
| Johnson County | 5 | 3.72% | 158,754 | 153,056 |
| Mills County | 6 | 2.99% | 14,829 | 14,398 |
| Wayne County | 7 | 2.75% | 6,691 | 6,512 |
| Taylor County | 8 | 2.73% | 6,022 | 5,862 |
| Lucas County | 9 | 2.54% | 8,837 | 8,618 |
| Shelby County | 10 | 2.22% | 11,996 | 11,735 |
| Marion County | 11 | 1.9% | 34,050 | 33,414 |
| Guthrie County | 12 | 1.81% | 10,804 | 10,612 |
| Dickinson County | 13 | 1.72% | 18,072 | 17,767 |
| Sioux County | 14 | 1.67% | 36,484 | 35,885 |
| Bremer County | 15 | 1.61% | 25,413 | 25,011 |
| Cherokee County | 16 | 1.54% | 11,835 | 11,656 |
| Benton County | 17 | 1.39% | 25,904 | 25,549 |
| Madison County | 18 | 1.23% | 16,833 | 16,629 |
| Clay County | 19 | 1.12% | 16,519 | 16,336 |
| Davis County | 20 | 1.12% | 9,213 | 9,111 |
| Van Buren County | 21 | 1% | 7,294 | 7,222 |
| Grundy County | 22 | 0.88% | 12,442 | 12,333 |
| Allamakee County | 23 | 0.82% | 14,186 | 14,071 |
| Woodbury County | 24 | 0.78% | 106,737 | 105,912 |
| Marshall County | 25 | 0.76% | 40,400 | 40,096 |
| Delaware County | 26 | 0.73% | 17,586 | 17,458 |
| Jones County | 27 | 0.72% | 20,802 | 20,653 |
| Harrison County | 28 | 0.56% | 14,650 | 14,569 |
| Story County | 29 | 0.54% | 99,184 | 98,649 |
| Buchanan County | 30 | 0.44% | 20,695 | 20,605 |
| Scott County | 31 | 0.4% | 175,308 | 174,609 |
| Washington County | 32 | 0.24% | 22,596 | 22,542 |
| Black Hawk County | 33 | 0.2% | 131,309 | 131,044 |
| Jasper County | 34 | 0.13% | 37,859 | 37,810 |
| Plymouth County | 35 | 0.12% | 25,722 | 25,692 |
| Wapello County | 36 | 0.03% | 35,336 | 35,326 |
| Decatur County | 37 | -0.01% | 7,605 | 7,606 |
| Cass County | 38 | -0.05% | 13,116 | 13,123 |
| Dubuque County | 39 | -0.08% | 99,231 | 99,308 |
| Pottawattamie County | 40 | -0.28% | 93,407 | 93,669 |
| Keokuk County | 41 | -0.28% | 9,976 | 10,004 |
| Boone County | 42 | -0.32% | 26,612 | 26,698 |
| Linn County | 43 | -0.6% | 229,036 | 230,419 |
| Calhoun County | 44 | -0.62% | 9,839 | 9,900 |
| Jackson County | 45 | -0.62% | 19,334 | 19,455 |
| Emmet County | 46 | -0.94% | 9,259 | 9,347 |
| Clinton County | 47 | -1% | 45,964 | 46,427 |
| Carroll County | 48 | -1.17% | 20,484 | 20,726 |
| Sac County | 49 | -1.21% | 9,680 | 9,799 |
| Mitchell County | 50 | -1.24% | 10,466 | 10,597 |
| Clayton County | 51 | -1.41% | 16,793 | 17,033 |
| Des Moines County | 52 | -1.41% | 38,275 | 38,823 |
| Humboldt County | 53 | -1.47% | 9,458 | 9,599 |
| Palo Alto County | 54 | -1.51% | 8,850 | 8,986 |
| Cerro Gordo County | 55 | -1.52% | 42,366 | 43,022 |
| Cedar County | 56 | -1.6% | 18,200 | 18,495 |
| Poweshiek County | 57 | -1.65% | 18,323 | 18,631 |
| Appanoose County | 58 | -1.73% | 12,075 | 12,287 |
| Fayette County | 59 | -1.78% | 19,098 | 19,445 |
| Union County | 60 | -1.81% | 11,912 | 12,132 |
| Monroe County | 61 | -1.86% | 7,452 | 7,593 |
| Buena Vista County | 62 | -1.89% | 20,413 | 20,806 |
| Ringgold County | 63 | -1.92% | 4,550 | 4,639 |
| Hancock County | 64 | -1.96% | 10,543 | 10,754 |
| O'Brien County | 65 | -2.01% | 13,866 | 14,150 |
| Winneshiek County | 66 | -2.02% | 19,641 | 20,045 |
| Floyd County | 67 | -2.06% | 15,282 | 15,604 |
| Winnebago County | 68 | -2.13% | 10,435 | 10,662 |
| Butler County | 69 | -2.16% | 14,024 | 14,333 |
| Fremont County | 70 | -2.16% | 6,424 | 6,566 |
| Mahaska County | 71 | -2.17% | 21,680 | 22,160 |
| Worth County | 72 | -2.25% | 7,269 | 7,436 |
| Webster County | 73 | -2.28% | 36,151 | 36,996 |
| Wright County | 74 | -2.62% | 12,578 | 12,916 |
| Clarke County | 75 | -2.66% | 9,478 | 9,737 |
| Franklin County | 76 | -2.69% | 9,733 | 10,002 |
| Tama County | 77 | -2.74% | 16,613 | 17,081 |
| Hamilton County | 78 | -2.85% | 14,581 | 15,008 |
| Muscatine County | 79 | -2.96% | 41,864 | 43,143 |
| Iowa County | 80 | -3.06% | 16,149 | 16,658 |
| Monona County | 81 | -3.15% | 8,467 | 8,742 |
| Adair County | 82 | -3.2% | 7,253 | 7,493 |
| Montgomery County | 83 | -3.25% | 9,997 | 10,333 |
| Page County | 84 | -3.29% | 14,690 | 15,190 |
| Kossuth County | 85 | -3.66% | 14,258 | 14,799 |
| Chickasaw County | 86 | -3.92% | 11,518 | 11,988 |
| Hardin County | 87 | -3.96% | 16,161 | 16,828 |
| Howard County | 88 | -3.99% | 9,110 | 9,489 |
| Pocahontas County | 89 | -4.01% | 6,782 | 7,065 |
| Audubon County | 90 | -4.06% | 5,452 | 5,683 |
| Crawford County | 91 | -4.26% | 15,781 | 16,484 |
| Lee County | 92 | -4.46% | 32,037 | 33,533 |
| Jefferson County | 93 | -4.52% | 14,984 | 15,694 |
| Louisa County | 94 | -4.71% | 10,305 | 10,814 |
| Ida County | 95 | -4.74% | 6,689 | 7,022 |
| Greene County | 96 | -4.8% | 8,332 | 8,752 |
| Osceola County | 97 | -6.58% | 5,790 | 6,198 |
| Adams County | 98 | -7.52% | 3,430 | 3,709 |
| Henry County | 99 | -11.31% | 18,135 | 20,447 |
Iowa's counties show varied growth patterns from 2020 to 2025. Dallas County leads with 16.36% annualized growth, followed by Warren County (8.4%) and Lyon County (5.77%). The largest counties are Polk County (513,397), Linn County (229,036), and Scott County (175,308). Of the 99 counties in Iowa, 36 are growing while 63 have experienced population decline. Overall, counties averaged -0.86% annualized growth, with total population growing by 0.96% annually.