Population of Counties in Iowa (2020)

In 2019, in the state of Iowa, the most populous county is Polk County, home to the city of Des Moines, which has a population of 478,204 people. Since the time of the last United States census in 2010, Polk County has seen a population growth rate of 12.68%. Following Polk County are Linn County with a population of 225,909 and a growth rate of 6.71%, Scott County with a population of 173,283 and a growth rate of 4.85%, and Johnson County with a population of 151,260 and a growth rate of 15.17%. The only other Iowa counties with more than 100,000 residents are Black Hawk County (132,408) and Woodbury County (102,539), both of which had modest growth of less than 1%. Johnson County had the highest growth rate of 15.17% since 2010.

Iowa Counties with the Fewest Residents

The Iowa county with the lowest population is Adams County, which has a population of just 3,648 as of 2019. This represents a decrease in the population of 9.4% since 2010. Behind Adams County are Ringgold County (4,968), Audubon County (5,506), and Osceola County (6,040). Iowa has 25 counties with fewer than 10,000 people. Of these counties, all have experienced a declining population except two -- Davis County (9,017) and Clarke County (9,423) -- with the greatest decline in Emmet County (-9.96).

Iowa Counties with Rapid Growth

The county in Iowa with the most rapid population growth is Dallas County. Since 2010, Dallas County has been the fastest-growing county in Iowa, growing an amazing 35.11% with the population now standing at 90,180 in 2019. Behind Dallas County in growth are Johnson County (15.17%), Polk County (12.68%), and Warren County (10.17%). Emmet County has seen the highest level of population loss with a growth rate of -9.96% since 2010.

Name 2020 Population Growth Since 2010
Polk County499,44015.51%
Linn County229,1738.26%
Scott County174,4655.56%
Johnson County155,35418.28%
Black Hawk County132,4060.95%
Woodbury County103,5131.10%
Story County99,79511.31%
Dubuque County96,5442.79%
Dallas County96,11043.99%
Pottawattamie County93,5790.23%
Warren County52,96414.29%
Clinton County45,750-6.82%
Muscatine County43,0030.59%
Cerro Gordo County41,947-4.87%
Marshall County39,647-2.64%
Des Moines County38,774-3.65%
Jasper County37,4711.79%
Webster County35,545-6.17%
Wapello County35,401-0.79%
Sioux County35,0453.83%
Marion County34,0112.37%
Lee County33,679-6.05%
Boone County26,086-0.72%
Benton County25,660-1.48%
Bremer County25,1973.71%
Plymouth County25,1030.52%
Washington County21,9091.01%
Mahaska County21,606-3.58%
Buchanan County21,2851.46%
Jones County20,8640.85%
Henry County20,081-0.12%
Carroll County19,916-4.36%
Winneshiek County19,825-5.93%
Fayette County19,564-6.21%
Jackson County19,560-1.35%
Buena Vista County19,418-4.60%
Poweshiek County18,9710.24%
Cedar County18,7791.49%
Jefferson County18,67710.93%
Clayton County17,368-3.94%
Crawford County17,2360.38%
Dickinson County17,1132.66%
Delaware County16,891-4.91%
Madison County16,6876.04%
Tama County16,602-6.30%
Hardin County16,590-5.43%
Iowa County16,187-0.91%
Clay County16,096-3.24%
Floyd County15,761-3.37%
Page County15,221-4.39%
Mills County15,0830.05%
Kossuth County14,784-4.77%
Hamilton County14,718-5.84%
Butler County14,453-3.14%
Harrison County14,144-5.13%
O'Brien County13,896-3.55%
Allamakee County13,888-3.41%
Appanoose County12,585-2.11%
Wright County12,572-4.65%
Cass County12,538-9.99%
Grundy County12,268-1.58%
Union County12,115-3.17%
Lyon County11,8392.34%
Chickasaw County11,820-4.75%
Shelby County11,580-4.88%
Cherokee County11,303-6.66%
Louisa County11,101-2.47%
Guthrie County10,826-1.01%
Hancock County10,590-6.26%
Mitchell County10,567-2.08%
Winnebago County10,378-4.30%
Keokuk County10,377-1.26%
Franklin County10,054-6.09%
Montgomery County9,787-8.45%
Clarke County9,6073.08%
Calhoun County9,599-5.52%
Sac County9,565-7.62%
Humboldt County9,485-3.15%
Howard County9,123-4.65%
Davis County9,0693.35%
Greene County9,005-3.81%
Emmet County8,931-13.09%
Lucas County8,835-0.71%
Palo Alto County8,669-7.77%
Monona County8,545-7.60%
Decatur County7,784-7.54%
Monroe County7,740-3.21%
Worth County7,437-1.93%
Adair County7,083-7.76%
Fremont County7,075-4.83%
Ida County6,811-3.62%
Van Buren County6,732-11.15%
Pocahontas County6,540-10.28%
Taylor County6,277-0.71%
Wayne County6,231-2.93%
Osceola County6,042-6.46%
Audubon County5,386-11.68%
Ringgold County4,846-5.22%
Adams County3,609-10.29%