| County | Rank | Change (2020) ↓ | 2026 Pop. | 2020 Pop. |
|---|---|---|---|---|
| Dallas County | 1 | 21.47% | 122,102 | 100,521 |
| Warren County | 2 | 10.59% | 58,166 | 52,597 |
| Polk County | 3 | 5.39% | 519,581 | 493,013 |
| Johnson County | 4 | 5.33% | 161,225 | 153,071 |
| Wayne County | 5 | 5.15% | 6,842 | 6,507 |
| Madison County | 6 | 4.57% | 17,391 | 16,631 |
| Jones County | 7 | 3.28% | 21,335 | 20,658 |
| Lyon County | 8 | 3.19% | 12,304 | 11,924 |
| Marion County | 9 | 3.02% | 34,429 | 33,420 |
| Mills County | 10 | 2.95% | 14,838 | 14,413 |
| Lucas County | 11 | 2.87% | 8,868 | 8,621 |
| Story County | 12 | 2.54% | 101,164 | 98,658 |
| Guthrie County | 13 | 2.48% | 10,877 | 10,614 |
| Sioux County | 14 | 2.46% | 36,771 | 35,888 |
| Benton County | 15 | 2.39% | 26,163 | 25,552 |
| Buchanan County | 16 | 2.17% | 21,055 | 20,608 |
| Davis County | 17 | 1.84% | 9,284 | 9,116 |
| Dickinson County | 18 | 1.73% | 18,082 | 17,775 |
| Delaware County | 19 | 1.66% | 17,746 | 17,456 |
| Linn County | 20 | 1.42% | 233,667 | 230,405 |
| Allamakee County | 21 | 1.41% | 14,270 | 14,072 |
| Mitchell County | 22 | 1.11% | 10,709 | 10,591 |
| Jasper County | 23 | 0.96% | 38,184 | 37,821 |
| Washington County | 24 | 0.87% | 22,732 | 22,536 |
| Bremer County | 25 | 0.86% | 25,229 | 25,014 |
| O'Brien County | 26 | 0.68% | 14,252 | 14,156 |
| Harrison County | 27 | 0.63% | 14,652 | 14,560 |
| Boone County | 28 | 0.62% | 26,871 | 26,705 |
| Scott County | 29 | 0.62% | 175,678 | 174,599 |
| Woodbury County | 30 | 0.57% | 106,556 | 105,949 |
| Black Hawk County | 31 | 0.42% | 131,591 | 131,037 |
| Dubuque County | 32 | 0.42% | 99,729 | 99,311 |
| Grundy County | 33 | 0.11% | 12,350 | 12,337 |
| Plymouth County | 34 | 0.05% | 25,710 | 25,697 |
| Ringgold County | 35 | -0.13% | 4,635 | 4,641 |
| Cedar County | 36 | -0.3% | 18,430 | 18,486 |
| Webster County | 37 | -0.32% | 36,877 | 36,997 |
| Fremont County | 38 | -0.37% | 6,551 | 6,575 |
| Taylor County | 39 | -0.6% | 5,827 | 5,862 |
| Iowa County | 40 | -0.79% | 16,534 | 16,665 |
| Worth County | 41 | -0.82% | 7,376 | 7,437 |
| Hamilton County | 42 | -0.83% | 14,890 | 15,014 |
| Clinton County | 43 | -0.92% | 46,005 | 46,431 |
| Palo Alto County | 44 | -0.93% | 8,906 | 8,990 |
| Wapello County | 45 | -0.97% | 34,991 | 35,334 |
| Greene County | 46 | -0.99% | 8,662 | 8,749 |
| Shelby County | 47 | -1.01% | 11,600 | 11,718 |
| Pottawattamie County | 48 | -1.01% | 92,722 | 93,667 |
| Howard County | 49 | -1.06% | 9,393 | 9,494 |
| Marshall County | 50 | -1.12% | 39,652 | 40,100 |
| Jackson County | 51 | -1.14% | 19,225 | 19,447 |
| Decatur County | 52 | -1.2% | 7,635 | 7,728 |
| Winneshiek County | 53 | -1.26% | 19,793 | 20,046 |
| Wright County | 54 | -1.28% | 12,754 | 12,919 |
| Mahaska County | 55 | -1.37% | 21,848 | 22,151 |
| Cerro Gordo County | 56 | -1.44% | 42,397 | 43,018 |
| Tama County | 57 | -1.54% | 16,788 | 17,050 |
| Cass County | 58 | -1.55% | 12,915 | 13,118 |
| Poweshiek County | 59 | -1.74% | 18,313 | 18,638 |
| Clarke County | 60 | -1.79% | 9,557 | 9,731 |
| Monona County | 61 | -1.83% | 8,586 | 8,746 |
| Crawford County | 62 | -1.83% | 16,185 | 16,487 |
| Clayton County | 63 | -1.88% | 16,707 | 17,027 |
| Appanoose County | 64 | -1.88% | 12,052 | 12,283 |
| Van Buren County | 65 | -2.02% | 7,075 | 7,221 |
| Adams County | 66 | -2.05% | 3,634 | 3,710 |
| Adair County | 67 | -2.09% | 7,341 | 7,498 |
| Keokuk County | 68 | -2.1% | 9,790 | 10,000 |
| Des Moines County | 69 | -2.18% | 38,004 | 38,849 |
| Hardin County | 70 | -2.26% | 16,450 | 16,831 |
| Butler County | 71 | -2.32% | 14,005 | 14,337 |
| Franklin County | 72 | -2.32% | 9,759 | 9,991 |
| Fayette County | 73 | -2.39% | 18,984 | 19,448 |
| Monroe County | 74 | -2.39% | 7,418 | 7,600 |
| Buena Vista County | 75 | -2.68% | 20,243 | 20,800 |
| Carroll County | 76 | -2.73% | 20,160 | 20,725 |
| Emmet County | 77 | -2.76% | 9,083 | 9,341 |
| Clay County | 78 | -2.8% | 15,883 | 16,341 |
| Humboldt County | 79 | -2.98% | 9,313 | 9,599 |
| Hancock County | 80 | -3.04% | 10,436 | 10,763 |
| Jefferson County | 81 | -3.26% | 15,177 | 15,688 |
| Union County | 82 | -3.26% | 11,734 | 12,130 |
| Chickasaw County | 83 | -3.28% | 11,602 | 11,995 |
| Ida County | 84 | -3.31% | 6,787 | 7,019 |
| Page County | 85 | -3.31% | 14,699 | 15,202 |
| Sac County | 86 | -3.63% | 9,436 | 9,791 |
| Audubon County | 87 | -3.7% | 5,470 | 5,680 |
| Montgomery County | 88 | -3.71% | 9,951 | 10,334 |
| Cherokee County | 89 | -3.71% | 11,216 | 11,648 |
| Muscatine County | 90 | -3.72% | 41,545 | 43,151 |
| Osceola County | 91 | -4.02% | 5,952 | 6,201 |
| Lee County | 92 | -4.16% | 32,132 | 33,527 |
| Kossuth County | 93 | -4.18% | 14,176 | 14,794 |
| Calhoun County | 94 | -4.3% | 9,470 | 9,895 |
| Winnebago County | 95 | -4.71% | 10,151 | 10,653 |
| Pocahontas County | 96 | -5.01% | 6,716 | 7,070 |
| Louisa County | 97 | -5.12% | 10,268 | 10,822 |
| Henry County | 98 | -5.48% | 19,330 | 20,450 |
| Floyd County | 99 | -5.6% | 14,721 | 15,595 |
Iowa's counties show varied growth patterns from 2020 to 2026. Dallas County leads with 3.29% annualized growth, followed by Warren County (1.69%) and Polk County (0.88%). The largest counties are Polk County (519,581), Linn County (233,667), and Scott County (175,678). Of the 99 counties in Iowa, 34 are growing while 65 have experienced population decline. Overall, counties averaged -0.1% annualized growth, with total population growing by 0.29% annually.
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