County outline
Where Marion County is located
Area breakdown
Land accounts for 97.2% of Marion County’s measured area and water for 2.8%. Its combined area converts to 1,477.6 square kilometers or approximately 365,124 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 554.49 | 1,436.123 | 354,873.6 |
| Water | 16.017 | 41.484 | 10,250.9 |
| Total | 570.507 | 1,477.606 | 365,124.5 |
How Marion County compares
By original Census land area, Marion County ranks #61 of 99 in Iowa and #1874 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.974 times the Iowa county-equivalent median of 569.6 square miles. It accounts for 1% of the combined county land area in the state.
See the complete Iowa ranking · What counts as a county equivalent?
Population and density of Marion County
The Census Bureau estimates that 34,192 people lived in Marion County on July 1, 2025. That ranks #1,370 of 3,222 county equivalents nationally and #21 of 99 in Iowa. Since the April 1, 2020 estimates base of 33,422, the population has grown by 770 (+2.3%), compared with +1.5% for Iowa as a whole.
With 554.5 square miles of land, that is 62 people per square mile (24 per km²), placing Marion County #1,365 nationally for density and #19 in Iowa. The median county equivalent has 47 people per square mile; the Iowa median is 26. Put another way, there are about 10 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 33,420 | 33,457 | 33,581 | 33,662 | 33,955 | 34,192 |
| Change | — | +37 | +124 | +81 | +293 | +237 |
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 Marion County
9 incorporated places lie at least partly in Marion County. Together they are home to 22,231 people (65%); the other 11,961 (35%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Pella city, with 10,992 residents in the county (the city extends into 1 other county). The county seat, Knoxville city, has 7,469 residents. Among places with at least 1,000 residents in 2020, Pella city grew fastest since then (+5.1%).
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Pella cityAlso in 1 other county | 10,992 | +5.1% | 9.343 |
| Knoxville cityCounty seat | 7,469 | −1.7% | 4.618 |
| Pleasantville city | 1,699 | +1.1% | 2.447 |
| Melcher-Dallas city | 1,196 | −0.3% | 1.04 |
| Bussey city | 379 | −0.3% | 0.311 |
| Harvey city | 246 | +2.9% | 0.677 |
| Hamilton city | 124 | +3.3% | 0.506 |
| Swan city | 79 | +3.9% | 0.617 |
| Marysville city | 47 | +2.2% | 0.539 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Marion County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Marion County is a central county of the Pella, IA Micropolitan Statistical Area. Marion County is the area’s only county equivalent, so the micro area has the same 554.5 square miles of land. By combined land it ranks #396 of 542 micropolitan areas, and #402 by population. It belongs to the Des Moines-West Des Moines-Ames, IA Combined Statistical Area.
ZIP codes
19 ZIP Code Tabulation Areas have land in Marion County; 12 of them have most of their land inside the county, and the others mainly cover neighboring areas.
50044500495005750062501165011950138501395014350150501635017050214502195022550228502375025250256
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 Marion County
Marion County shares a land border with 6 county equivalents. It has more land than 2 of them. The largest neighbor is Jasper County (730.4 mi²) and the smallest is Lucas County (430.7 mi²). Together with its neighbors, Marion County forms a block of 3,862.5 mi² of land, of which it holds 14.4%.
| Bordering county equivalent | Land mi² | Size vs. Marion | Compare |
|---|---|---|---|
| Jasper County | 730.4 | 1.3× larger | Compare |
| Polk County | 572.7 | about the same | Compare |
| Mahaska County | 570.9 | about the same | Compare |
| Warren County | 569.7 | about the same | Compare |
| Monroe County | 433.7 | 1.3× smaller | Compare |
| Lucas County | 430.7 | 1.3× smaller | Compare |
How big is Marion County compared with U.S. states?
Marion County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.9 times as much. Iowa’s county land could hold about 101 areas the size of Marion County.
Another way to picture it: the same land area would fill a square about 23.5 miles (37.9 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 Marion County?
Marion County has more land than 1,348 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 Marion County at #1,927 nationally by total area, 53 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 2.8%, compared with a national county-equivalent median of 1.2% — 1.6 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 Marion County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1873 | Franklin County, Tennessee | 554.5 | Compare |
| #1874 | Marion County, Iowa | 554.5 | This county |
| #1875 | Hennepin County, Minnesota | 554 | Compare |
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.
Representative coordinates
The Census internal point is 41.331432, -93.093868. It represents a location inside the geography; it is not necessarily the centroid or the address of a courthouse.
Source and precision
U.S. Census Bureau, 2026 Gazetteer Files, Counties. Original ALAND: 1,436,123,088 m²; AWATER: 41,484,605 m². Rankings use ALAND; exact ties use ascending GEOID. Tables preserve Census-published square miles to three decimals, with conversions based on those values.
Common questions
How big is Marion County?
Marion County, Iowa has 554.5 square miles (1,436.1 km²) of land and 16 square miles of water, for a total area of 570.5 square miles. It ranks #1874 of 3,222 U.S. county equivalents by land area.
Is Marion County the largest county in Iowa?
No. Marion County ranks #61 of 99 in Iowa by land area. The largest is Kossuth County, with 972.7 square miles of land.
What counties border Marion County?
Marion County shares a land border with Mahaska County, Jasper County, Warren County, Lucas County, Monroe County, and Polk County.
What is the population of Marion County?
The Census Bureau estimates Marion County had 34,192 residents on July 1, 2025, ranking #1,370 of 3,222 county equivalents. That is 62 people per square mile of land.
What is the county seat of Marion County?
The county seat of Marion County is Knoxville.
What cities and towns are in Marion County?
Marion County has 9 incorporated places. The most populous five are Pella city, Knoxville city, Pleasantville city, Melcher-Dallas city, and Bussey city; 11,961 residents live outside any incorporated place.
Is Marion County part of a metropolitan area?
Yes. It is a central county of the Pella, IA Micropolitan Statistical Area.
How many ZIP codes are in Marion County?
19 ZIP Code Tabulation Areas have land in Marion County, and 12 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Marion County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.9 times as much land.
How many acres of land are in Marion County?
The land measurement converts to approximately 354,874 acres. Including water, total area is approximately 365,124 acres. One square mile equals 640 acres.
Why might another source show a different area?
Check whether it reports land or total area, its Census vintage, and its rounding. Our guide explains how to reconcile county area figures.
Can this establish a property boundary?
No. Statistical measurements and generalized maps do not establish property lines. Consult the relevant local surveying or land-records authority.