County outline
Where Ottawa County is located
Area breakdown
Land accounts for 43.5% of Ottawa County’s measured area and water for 56.5%. Its combined area converts to 1,515.3 square kilometers or approximately 374,449 acres.
Green: land · blue: water
| Measurement | Square miles | Square kilometers | Acres |
|---|---|---|---|
| Land | 254.685 | 659.631 | 162,998.4 |
| Water | 330.392 | 855.711 | 211,450.9 |
| Total | 585.077 | 1,515.342 | 374,449.3 |
How Ottawa County compares
By original Census land area, Ottawa County ranks #86 of 88 in Ohio and #2897 of 3,222 nationally. National rankings include the 50 states, District of Columbia, and Puerto Rico.
Its land area is 0.584 times the Ohio county-equivalent median of 436 square miles. It accounts for 0.6% of the combined county land area in the state.
See the complete Ohio ranking · What counts as a county equivalent?
Population and density of Ottawa County
The Census Bureau estimates that 39,481 people lived in Ottawa County on July 1, 2025. That ranks #1,223 of 3,222 county equivalents nationally and #62 of 88 in Ohio. Since the April 1, 2020 estimates base of 40,367, the population has declined by 886 (−2.2%), compared with +0.9% for Ohio as a whole.
With 254.7 square miles of land, that is 155 people per square mile (60 per km²), placing Ottawa County #760 nationally for density and #34 in Ohio. The median county equivalent has 47 people per square mile; the Ohio median is 120. Put another way, there are about 4.1 acres of land per resident.
| July 1 | 2020 | 2021 | 2022 | 2023 | 2024 | 2025 |
|---|---|---|---|---|---|---|
| Estimate | 40,303 | 40,143 | 39,945 | 39,810 | 39,729 | 39,481 |
| Change | — | −160 | −198 | −135 | −81 | −248 |
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 Ottawa County
8 incorporated places lie at least partly in Ottawa County. Together they are home to 13,723 people (34.8%); the other 25,758 (65.2%) live outside any incorporated place, in unincorporated communities and rural areas.
The largest is Port Clinton city, with 5,875 residents in the county. By land, Marblehead village is the largest at 3.17 mi².
| Incorporated place | Population 2025 | Since 2020 | Land mi² |
|---|---|---|---|
| Port Clinton cityCounty seat | 5,875 | −2.5% | 2.131 |
| Oak Harbor village | 2,780 | −1.5% | 1.588 |
| Genoa village | 2,167 | −2.9% | 2.144 |
| Elmore villageAlso in 1 other county | 1,370 | −2.8% | 0.882 |
| Marblehead village | 829 | −2.4% | 3.17 |
| Rocky Ridge village | 303 | −2.6% | 1.002 |
| Clay Center village | 247 | −5.4% | 1.013 |
| Put-in-Bay village | 152 | −2.6% | 0.435 |
Population: U.S. Census Bureau Vintage 2025 subcounty estimates, counting only the part of each place inside Ottawa County. Land: 2026 Census Gazetteer, for the whole place even where it extends into other counties. How communities are listed.
Metropolitan area
Ottawa County is a central county of the Sandusky, OH Metropolitan Statistical Area. Its 2 county equivalents have 112,777 residents on 506 square miles of land; Ottawa County accounts for 50.3% of the land and 35% of the residents. By combined land it ranks #359 of 393 metropolitan areas, and #347 by population. It belongs to the Cleveland-Akron-Canton, OH Combined Statistical Area.
| County equivalent | Population 2025 | Land mi² |
|---|---|---|
| Erie County | 73,296 | 251.3 |
| Ottawa County | 39,481 | 254.7 |
ZIP codes
20 ZIP Code Tabulation Areas have land in Ottawa County; 15 of them have most of their land inside the county, and the others mainly cover neighboring areas.
4340843412434164342043430434324343343436434394344043442434454344643447434494345243456434584346843469
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 Ottawa County
Ottawa County shares a land border with 3 county equivalents. Each of them has more land than Ottawa County. The largest neighbor is Wood County (617.2 mi²) and the smallest is Lucas County (339.7 mi²). Together with its neighbors, Ottawa County forms a block of 1,619.8 mi² of land, of which it holds 15.7%.
| Bordering county equivalent | Land mi² | Size vs. Ottawa | Compare |
|---|---|---|---|
| Wood County | 617.2 | 2.4× larger | Compare |
| Sandusky County | 408.2 | 1.6× larger | Compare |
| Lucas County | 339.7 | 1.3× larger | Compare |
How big is Ottawa County compared with U.S. states?
Ottawa County has less land than any of the 50 states. Rhode Island, the smallest state by land area, has 1,033.9 mi², about 4.1 times as much. Ohio’s county land could hold about 160 areas the size of Ottawa County.
Another way to picture it: the same land area would fill a square about 16 miles (25.7 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 Ottawa County?
Ottawa County has more land than 325 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 Ottawa County at #1,804 nationally by total area, 1,093 places closer to the top than its land rank. The water assigned to this geography moves it ahead of some county equivalents with more land.
Its water share is 56.5%, compared with a national county-equivalent median of 1.2% — 55.3 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 Ottawa County in the national ranking. They can be in different states and are not necessarily geographic neighbors.
| Land rank | County equivalent | Land mi² | Comparison |
|---|---|---|---|
| #2896 | Lee County, North Carolina | 255.1 | Compare |
| #2897 | Ottawa County, Ohio | 254.7 | This county |
| #2898 | Sagadahoc County, Maine | 254 | 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 41.545495, -83.012613. 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: 659,630,337 m²; AWATER: 855,711,479 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 Ottawa County?
Ottawa County, Ohio has 254.7 square miles (659.6 km²) of land and 330.4 square miles of water, for a total area of 585.1 square miles. It ranks #2897 of 3,222 U.S. county equivalents by land area.
Is Ottawa County the largest county in Ohio?
No. Ottawa County ranks #86 of 88 in Ohio by land area. The largest is Ashtabula County, with 702.4 square miles of land.
What counties border Ottawa County?
Ottawa County shares a land border with Sandusky County, Lucas County, and Wood County.
What is the population of Ottawa County?
The Census Bureau estimates Ottawa County had 39,481 residents on July 1, 2025, ranking #1,223 of 3,222 county equivalents. That is 155 people per square mile of land.
What is the county seat of Ottawa County?
The county seat of Ottawa County is Port Clinton.
What cities and towns are in Ottawa County?
Ottawa County has 8 incorporated places. The most populous five are Port Clinton city, Oak Harbor village, Genoa village, Elmore village, and Marblehead village; 25,758 residents live outside any incorporated place.
Is Ottawa County part of a metropolitan area?
Yes. It is a central county of the Sandusky, OH Metropolitan Statistical Area, which has 2 county equivalents and 112,777 residents.
How many ZIP codes are in Ottawa County?
20 ZIP Code Tabulation Areas have land in Ottawa 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 Ottawa County compare with U.S. states?
It has less land than every state. Rhode Island, the smallest, has 4.1 times as much land.
How many acres of land are in Ottawa County?
The land measurement converts to approximately 162,998 acres. Including water, total area is approximately 374,449 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.