There are 99 counties in Iowa. 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.
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).
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.