County outline
Where Marion County is located
Area breakdown
Land accounts for 99.9% of Marion County’s measured area and water for 0.1%. Its combined area converts to 1,046.8 square kilometers or approximately 258,661 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 403.807 | 1,045.855 | 258,436.5 |
| Water | 0.351 | 0.909 | 224.6 |
| Total | 404.158 | 1,046.764 | 258,661.1 |
How Marion County compares
By original Census land area, Marion County ranks #75 of 88 in Ohio and #2506 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.926 times the Ohio county-equivalent median of 436 square miles. It accounts for 1% of the combined county land area in the state.
See the complete Ohio ranking · What counts as a county equivalent?
Population and density of Marion County
The Census Bureau estimates that 65,115 people lived in Marion County on July 1, 2025. That ranks #854 of 3,222 county equivalents nationally and #37 of 88 in Ohio. Since the April 1, 2020 estimates base of 65,352, the population has declined by 237 (−0.4%), compared with +0.9% for Ohio as a whole.
With 403.8 square miles of land, that is 161 people per square mile (62 per km²), placing Marion County #742 nationally for density and #32 in Ohio. The median county equivalent has 47 people per square mile; the Ohio median is 120. Put another way, there are about 4 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 65,385 | 65,285 | 64,538 | 64,768 | 64,877 | 65,115 |
| Change | — | −100 | −747 | +230 | +109 | +238 |
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
8 incorporated places lie at least partly in Marion County. Together they are home to 39,286 people (60.3%); the other 25,829 (39.7%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Marion city, with 35,587 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Marion cityCounty seat | 35,587 | −1.3% | 13 |
| Prospect village | 1,056 | −1.4% | 0.724 |
| La Rue village | 674 | −1.2% | 0.478 |
| Caledonia village | 559 | −0.5% | 0.242 |
| New Bloomington village | 418 | +1% | 0.44 |
| Morral village | 367 | −1.9% | 2.701 |
| Waldo village | 320 | −0.6% | 0.648 |
| Green Camp village | 305 | −1.3% | 0.338 |
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 Marion, OH Micropolitan Statistical Area. Marion County is the area’s only county equivalent, so the micro area has the same 403.8 square miles of land. By combined land it ranks #486 of 542 micropolitan areas, and #141 by population. It belongs to the Columbus-Marion-Zanesville, OH Combined Statistical Area.
ZIP codes
14 ZIP Code Tabulation Areas have land in Marion County; 8 of them have most of their land inside the county, and the others mainly cover neighboring areas.
4330243314433154332243323433264333243337433414334243344433564483344849
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 1 of them. The largest neighbor is Hardin County (470.3 mi²) and the smallest is Crawford County (401.8 mi²). Together with its neighbors, Marion County forms a block of 2,963.8 mi² of land, of which it holds 13.6%.
| Bordering county equivalent | Land mi² | Size vs. Marion | Compare |
|---|---|---|---|
| Hardin County | 470.3 | 1.2× larger | Compare |
| Delaware County | 443.1 | 1.1× larger | Compare |
| Union County | 431.7 | 1.1× larger | Compare |
| Wyandot County | 406.9 | about the same | Compare |
| Morrow County | 406.1 | about the same | Compare |
| Crawford County | 401.8 | about the same | 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 2.6 times as much. Ohio’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 20.1 miles (32.3 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 716 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 #2,584 nationally by total area, 78 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 0.1%, compared with a national county-equivalent median of 1.2% — 1.1 percentage points lower. 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 |
|---|---|---|---|
| #2505 | Morgan County, Indiana | 403.9 | Compare |
| #2506 | Marion County, Ohio | 403.8 | This county |
| #2507 | Vigo County, Indiana | 403.6 | 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 40.588034, -83.168803. 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: 1,045,855,304 m²; AWATER: 908,577 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, Ohio has 403.8 square miles (1,045.9 km²) of land and 0.351 square miles of water, for a total area of 404.2 square miles. It ranks #2506 of 3,222 U.S. county equivalents by land area.
Is Marion County the largest county in Ohio?
No. Marion County ranks #75 of 88 in Ohio by land area. The largest is Ashtabula County, with 702.4 square miles of land.
What counties border Marion County?
Marion County shares a land border with Morrow County, Wyandot County, Union County, Crawford County, Hardin County, and Delaware County.
What is the population of Marion County?
The Census Bureau estimates Marion County had 65,115 residents on July 1, 2025, ranking #854 of 3,222 county equivalents. That is 161 people per square mile of land.
What is the county seat of Marion County?
The county seat of Marion County is Marion.
What cities and towns are in Marion County?
Marion County has 8 incorporated places. The most populous five are Marion city, Prospect village, La Rue village, Caledonia village, and New Bloomington village; 25,829 residents live outside any incorporated place.
Is Marion County part of a metropolitan area?
Yes. It is a central county of the Marion, OH Micropolitan Statistical Area.
How many ZIP codes are in Marion County?
14 ZIP Code Tabulation Areas have land in Marion County, and 8 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 2.6 times as much land.
How many acres of land are in Marion County?
The land measurement converts to approximately 258,436 acres. Including water, total area is approximately 258,661 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.