County Maps US

Mercer County, Ohio

A county in Ohio, ranked 57 of 88 by population.

CountyFIPS 39107

Within Ohio
Mercer County, highlighted, with the areas around it. Boundaries generalised from the 2025 Census cartographic boundary file; neighbour fills carry no data. The dot marks Celina, the county seat, located via the 2025 Census Gazetteer.

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Population
42,737
+203 (+0.5%) since 2020
Land area
462.4
square miles. A further 2.3% of the total area is water
Population density
92.4
people per square mile, computed rather than published
County seat
Celina
Seat of county government.
Established
1824
201 years ago
Largest city
Celina city
Population 10,936.

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; Wikidata (CC0), Wikidata. Retrieved 30 August 2026.

Satellite view

Aerial imagery of Mercer County with its boundary drawn on top. A map shows you the shape; this shows you what is inside it, and which side of the line a place falls on.

Aerial view of Mercer County, Ohio from the USGS National Map, with its boundary outlined
Imagery: USGS National Map, USGS Imagery Only, public domain, requested from USGS by your browser when you reach this point on the page, at 623 by 800 pixels. The boundary is the 2025 Census cartographic boundary file, reprojected to Web Mercator to match the imagery. You can also open the USGS National Map viewer.

Where Mercer County ranks

Position among the 88 counties of Ohio, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn OhioNationally
Population42,73757th of 881,141st of 3,144
Land area462.4 sq mi36th of 882,221st of 3,144
Population density92.4 per sq mi59th of 88970th of 3,144
Median household income$76,78217th of 88736th of 3,143

Full data for Mercer County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population42,737Vintage 2025 Population Estimates
Population in 202042,534Vintage 2025 Population Estimates
2020 estimates base?42,529Vintage 2025 Population Estimates
Land area462.4 sq mi2025 Gazetteer Files
Water area11.0 sq mi2025 Gazetteer Files
Total area473.4 sq mi2025 Gazetteer Files
Population density?92.4 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$76,782American Community Survey 2020-2024 5-Year Estimates
Median home value$210,600American Community Survey 2020-2024 5-Year Estimates
Median age39.4American Community Survey 2020-2024 5-Year Estimates
Households16,408American Community Survey 2020-2024 5-Year Estimates
Housing units18,103American Community Survey 2020-2024 5-Year Estimates

Sources: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026; US Census Bureau, Gazetteer Files, 2025 Gazetteer Files, released 10 September 2025; US Census Bureau, American Community Survey, American Community Survey 2020-2024 5-Year Estimates, released 29 January 2026. Population density is computed here, not published: it divides the Vintage 2025 population estimate by the 2025 Gazetteer land area, which are two different Census products. Retrieved 30 August 2026.

How the population changed

The Census Bureau publishes the components behind an estimate, not just the total. For the year to July 2025:

Births minus deaths
+203
635 births, 432 deaths
Net migration
+12
More people moved in than moved out.

Source: US Census Bureau, Population Estimates Program, Vintage 2025 Population Estimates, released 26 March 2026. Retrieved 30 August 2026.

The 6 areas bordering Mercer County

Ordered by the length of the border actually shared, which the Census Bureau publishes in its county adjacency file and which no other county reference presents.

Bordering areaStateShared borderPopulation
Auglaize CountyOhio24 mi45,909
Van Wert CountyOhio21 mi29,013
Darke CountyOhio20 mi51,520
Jay CountyIndiana15 mi20,118
Adams CountyIndiana11 mi36,650
Shelby CountyOhio0.3 mi48,065

Source: US Census Bureau, County Adjacency File, 2025 County Adjacency File, released 15 September 2025. Retrieved 30 August 2026.

All 88 counties of Ohio

Open the interactive Ohio county map, or jump straight to any of them.

Data on this page last rebuilt 30 August 2026. How these figures are produced.