Polk County area

Population and density of Polk County

The Census Bureau estimates that 516,546 people lived in Polk County on July 1, 2025. That ranks #145 of 3,222 county equivalents nationally and #1 of 99 in Iowa. Since the April 1, 2020 estimates base of 492,389, the population has grown by 24,157 (+4.9%), compared with +1.5% for Iowa as a whole.

With 572.7 square miles of land, that is 902 people per square mile (348 per km²), placing Polk County #205 nationally for density and #1 in Iowa. The median county equivalent has 47 people per square mile; the Iowa median is 26. Put another way, there are about 0.71 acres of land per resident.

U.S. Census Bureau, Vintage 2025 population estimates. Estimates are revised each year and are not decennial census counts. Density divides the whole population by the whole county’s land area, so it describes an average, not how settlement is distributed within the county. Population sources and methods.

Cities and towns in Polk County

20 incorporated places lie at least partly in Polk County. Together they are home to 488,349 people (94.5%); the other 28,197 (5.5%) live outside any incorporated place, in unincorporated communities and rural areas.

The largest is Des Moines city, with 211,882 residents in the county (the city extends into 1 other county). Among places with at least 1,000 residents in 2020, Bondurant city grew fastest since then (+30.3%).

Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Polk County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.

Metropolitan area

Polk County is a central county of the Des Moines-West Des Moines, IA Metropolitan Statistical Area. Its 6 county equivalents have 758,539 residents on 3,612.7 square miles of land; Polk County accounts for 15.9% of the land and 68.1% of the residents. By combined land it ranks #80 of 393 metropolitan areas, and #83 by population. It belongs to the Des Moines-West Des Moines-Ames, IA Combined Statistical Area.

ZIP codes

42 ZIP Code Tabulation Areas have land in Polk County; 32 of them have most of their land inside the county, and the others mainly cover neighboring areas.

500075000950021500235003250035500465004750061500735010950111501245013150156501615016850169502265022850237502435024450265502665030950310503115031250313503145031550316503175031950320503215032250323503245032550327

ZIP Code Tabulation Areas are the Census Bureau’s approximations of USPS ZIP Code service areas, from the 2020 Census relationship files. Lighter codes have less than half of their land in this county. Post-office-box and single-address ZIP Codes have no tabulation area.

Counties bordering Polk County

Polk County shares a land border with 6 county equivalents. It has more land than 4 of them. The largest neighbor is Jasper County (730.4 mi²) and the smallest is Marion County (554.5 mi²). Together with its neighbors, Polk County forms a block of 4,158.5 mi² of land, of which it holds 13.8%.

How big is Polk County compared with U.S. states?

Polk County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.8 times as much. Iowa’s county land could hold about 98 areas the size of Polk County.

Another way to picture it: the same land area would fill a square about 23.9 miles (38.5 km) on each side. Real county shapes are rarely square, so this is a scale reference rather than a width or driving distance.

State figures are the sums of each state’s county-equivalent land measurements in the same Census release, so states and counties are compared on the same basis. Published state totals can differ slightly because of rounding. Compare all states · Counties bigger than entire states.

What stands out about Polk County?

Polk County has more land than 1,477 of the other 3,221 county equivalents in the dataset.

A median is the middle county-equivalent measurement, not the average of the largest and smallest. All three bars use the same linear scale. Very small areas may appear as a thin sliver; the labels retain their values.

Does including water change its rank?

Using land plus water places Polk County at #1,772 nationally by total area, 27 places farther from the top than its land rank. Other county equivalents gain more area when their water measurements are included.

Its water share is 3.2%, compared with a national county-equivalent median of 1.2% — 2.1 percentage points higher. This describes the statistical geography’s land/water mix, not flood exposure or developable land.

Closest positions in the national land ranking

These entries sit immediately beside Polk County in the national ranking. They can be in different states and are not necessarily geographic neighbors.

Calculated from the same Census release as the area table. Total-area order uses original ALAND + AWATER; water shares and chart labels use published square miles. Calculation details.