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What are the largest counties in Iowa?

Polk County is the largest county in Iowa, with 516,546 residents in 2025 (Census PEP). Linn County (232,028) and Scott County (175,259) come next.

Data as of 2025 · updated

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All 99 ranked Iowa counties

Iowa counties ranked by population
RankCountyResidents 2025Change 2020–25
1Polk County516,546+4.8%
2Linn County232,028+0.7%
3Scott County175,259+0.4%
4Johnson County160,044+4.6%
5Black Hawk County131,532+0.4%
6Dallas County118,457+17.8%
7Woodbury County106,649+0.7%
8Story County101,291+2.7%
9Dubuque County99,381+0.1%
10Pottawattamie County92,996−0.7%
11Warren County57,331+9.0%
12Clinton County46,002−0.9%
13Cerro Gordo County42,372−1.5%
14Muscatine County41,853−3.0%
15Marshall County39,890−0.5%
16Jasper County38,153+0.9%
17Des Moines County38,077−2.0%
18Webster County36,838−0.4%
19Sioux County36,774+2.5%
20Wapello County35,210−0.4%
21Marion County34,192+2.3%
22Lee County32,306−3.6%
23Boone County26,799+0.4%
24Benton County26,004+1.8%
25Plymouth County25,697+0.0%
26Bremer County25,296+1.1%
27Washington County22,667+0.6%
28Mahaska County21,880−1.2%
29Jones County21,253+2.9%
30Buchanan County20,883+1.3%
31Buena Vista County20,449−1.7%
32Carroll County20,303−2.0%
33Winneshiek County19,733−1.6%
34Henry County19,349−5.4%
35Jackson County19,288−0.8%
36Fayette County19,047−2.1%
37Poweshiek County18,368−1.4%
38Cedar County18,359−0.7%
39Dickinson County18,077+1.7%
40Delaware County17,674+1.2%
41Madison County17,270+3.8%
42Clayton County16,845−1.1%
43Tama County16,796−1.5%
44Iowa County16,504−1.0%
45Hardin County16,455−2.2%
46Crawford County16,237−1.5%
47Clay County16,202−0.9%
48Jefferson County15,291−2.5%
49Hamilton County14,944−0.5%
50Floyd County14,901−4.5%
51Page County14,856−2.3%
52Mills County14,793+2.6%
53Harrison County14,623+0.4%
54Kossuth County14,322−3.2%
55Allamakee County14,238+1.2%
56O'Brien County14,220+0.5%
57Butler County14,049−2.0%
58Cass County12,960−1.2%
59Wright County12,801−0.9%
60Grundy County12,361+0.2%
61Lyon County12,354+3.6%
62Appanoose County12,077−1.7%
63Union County11,829−2.5%
64Shelby County11,689−0.2%
65Chickasaw County11,663−2.8%
66Cherokee County11,369−2.4%
67Guthrie County10,782+1.6%
68Mitchell County10,650+0.6%
69Hancock County10,528−2.2%
70Louisa County10,416−3.8%
71Winnebago County10,251−3.8%
72Montgomery County10,002−3.2%
73Franklin County9,868−1.2%
74Keokuk County9,797−2.0%
75Clarke County9,574−1.6%
76Calhoun County9,562−3.4%
77Sac County9,525−2.7%
78Howard County9,415−0.8%
79Humboldt County9,409−2.0%
80Davis County9,230+1.3%
81Emmet County9,107−2.5%
82Palo Alto County8,899−1.0%
83Lucas County8,847+2.6%
84Greene County8,658−1.0%
85Monona County8,539−2.4%
86Decatur County7,655−0.9%
87Monroe County7,406−2.6%
88Adair County7,403−1.3%
89Worth County7,338−1.3%
90Van Buren County7,131−1.2%
91Pocahontas County6,819−3.6%
92Ida County6,777−3.4%
93Wayne County6,738+3.6%
94Fremont County6,522−0.8%
95Osceola County5,980−3.6%
96Taylor County5,835−0.5%
97Audubon County5,509−3.0%
98Ringgold County4,642+0.0%
99Adams County3,617−2.5%

How this is ranked

The Census Bureau's July 1 resident population estimates for 2025, largest first, with the change since 2020. Counties with fewer than 1,000 residents are not ranked. Areas without an estimate for the same year as the others are not ranked.

Source: U.S. Census Bureau, Population Estimates Program (Vintage 2025). Figures come from public federal statistics and are informational only, not investment advice. Check the source before relying on a number. Methodology: how ranks and figures are built.

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Questions

What is the largest county in Iowa?

Polk County is the largest county in Iowa, with 516,546 residents in 2025 (Census PEP). Linn County (232,028) and Scott County (175,259) come next.

How is this ranking calculated?

The Census Bureau's July 1 resident population estimates for 2025, largest first, with the change since 2020. Counties with fewer than 1,000 residents are not ranked. Areas without an estimate for the same year as the others are not ranked.

More rankings for Iowa

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Across the U.S.