County outline
Where Washington County is located
Area breakdown
Land accounts for 98.8% of Washington County’s measured area and water for 1.2%. Its combined area converts to 1,658.3 square kilometers or approximately 409,763 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 632.276 | 1,637.587 | 404,656.6 |
| Water | 7.979 | 20.666 | 5,106.6 |
| Total | 640.255 | 1,658.253 | 409,763.2 |
How Washington County compares
By original Census land area, Washington County ranks #5 of 88 in Ohio and #1513 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 1.45 times the Ohio county-equivalent median of 436 square miles. It accounts for 1.5% of the combined county land area in the state.
See the complete Ohio ranking · What counts as a county equivalent?
Population and density of Washington County
The Census Bureau estimates that 58,389 people lived in Washington County on July 1, 2025. That ranks #924 of 3,222 county equivalents nationally and #44 of 88 in Ohio. Since the April 1, 2020 estimates base of 59,773, the population has declined by 1,384 (−2.3%), compared with +0.9% for Ohio as a whole.
With 632.3 square miles of land, that is 92 people per square mile (36 per km²), placing Washington County #1,049 nationally for density and #60 in Ohio. The median county equivalent has 47 people per square mile; the Ohio median is 120. Put another way, there are about 6.9 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 59,657 | 59,485 | 58,890 | 58,637 | 58,599 | 58,389 |
| Change | — | −172 | −595 | −253 | −38 | −210 |
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 Washington County
7 incorporated places lie at least partly in Washington County. Together they are home to 22,338 people (38.3%); the other 36,051 (61.7%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Marietta city, with 13,053 residents in the county.
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Marietta cityCounty seat | 13,053 | −2.5% | 8.429 |
| Belpre city | 6,657 | −1% | 3.485 |
| Beverly village | 1,200 | −2.8% | 0.682 |
| Matamoras (New Matamoras) village | 690 | −2.7% | 0.348 |
| Lowell village | 552 | −2.3% | 0.228 |
| Macksburg village | 114 | −2.6% | 0.216 |
| Lower Salem village | 72 | −2.7% | 0.059 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Washington County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Washington County is a central county of the Marietta, OH Micropolitan Statistical Area. Washington County is the area’s only county equivalent, so the micro area has the same 632.3 square miles of land. By combined land it ranks #336 of 542 micropolitan areas, and #173 by population. It belongs to the Parkersburg-Marietta-Vienna, WV-OH Combined Statistical Area.
ZIP codes
21 ZIP Code Tabulation Areas have land in Washington County; 15 of them have most of their land inside the county, and the others mainly cover neighboring areas.
437874571145714457154572145723457244572745729457424574445745457464575045767457684577345784457864578845789
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 Washington County
Washington County shares a land border with 7 county equivalents, including 3 in West Virginia. It has more land than every one of them. The largest neighbor is Athens County (504.1 mi²) and the smallest is Pleasants County (130.1 mi²). Together with its neighbors, Washington County forms a block of 3,159.3 mi² of land, of which it holds 20%.
| Bordering county equivalent | Land mi² | Size vs. Washington | Compare |
|---|---|---|---|
| Athens County | 504.1 | 1.3× smaller | Compare |
| Monroe County | 455.6 | 1.4× smaller | Compare |
| Morgan County | 416.4 | 1.5× smaller | Compare |
| Noble County | 398 | 1.6× smaller | Compare |
| Wood CountyWest Virginia | 366.5 | 1.7× smaller | Compare |
| Tyler CountyWest Virginia | 256.3 | 2.5× smaller | Compare |
| Pleasants CountyWest Virginia | 130.1 | 4.9× smaller | Compare |
How big is Washington County compared with U.S. states?
Washington County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 1.6 times as much. Ohio’s county land could hold about 65 areas the size of Washington County.
Another way to picture it: the same land area would fill a square about 25.1 miles (40.5 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 Washington County?
Washington County has more land than 1,709 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 Washington County at #1,613 nationally by total area, 100 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 1.2%, compared with a national county-equivalent median of 1.2%. The two percentages are within 0.1 percentage points of each other. 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 Washington County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #1512 | Cotton County, Oklahoma | 632.6 | Compare |
| #1513 | Washington County, Ohio | 632.3 | This county |
| #1514 | Taney County, Missouri | 632.3 | 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 39.450602, -81.490538. 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: 1,637,585,960 m²; AWATER: 20,665,109 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 Washington County?
Washington County, Ohio has 632.3 square miles (1,637.6 km²) of land and 7.979 square miles of water, for a total area of 640.3 square miles. It ranks #1513 of 3,222 U.S. county equivalents by land area.
Is Washington County the largest county in Ohio?
No. Washington County ranks #5 of 88 in Ohio by land area. The largest is Ashtabula County, with 702.4 square miles of land.
What counties border Washington County?
Washington County shares a land border with Wood County, West Virginia, Morgan County, Athens County, Noble County, Monroe County, Pleasants County, West Virginia, and Tyler County, West Virginia.
What is the population of Washington County?
The Census Bureau estimates Washington County had 58,389 residents on July 1, 2025, ranking #924 of 3,222 county equivalents. That is 92 people per square mile of land.
What is the county seat of Washington County?
The county seat of Washington County is Marietta.
What cities and towns are in Washington County?
Washington County has 7 incorporated places. The most populous five are Marietta city, Belpre city, Beverly village, Matamoras (New Matamoras) village, and Lowell village; 36,051 residents live outside any incorporated place.
Is Washington County part of a metropolitan area?
Yes. It is a central county of the Marietta, OH Micropolitan Statistical Area.
How many ZIP codes are in Washington County?
21 ZIP Code Tabulation Areas have land in Washington County, and 15 of them have most of their land inside the county. Census ZIP Code Tabulation Areas approximate USPS ZIP Code areas.
How does Washington County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 1.6 times as much land.
How many acres of land are in Washington County?
The land measurement converts to approximately 404,657 acres. Including water, total area is approximately 409,763 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.