County Maps US

Miami County, Ohio

A county in Ohio, ranked 25 of 88 by population.

CountyFIPS 39109

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

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Population
112,634
+3,660 (+3.4%) since 2020
Land area
406.6
square miles. A further 0.7% of the total area is water
Population density
277
people per square mile, computed rather than published
County seat
Troy
Seat of county government.
Established
1807
218 years ago
Largest city
Troy city
Population 27,344.

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 Miami 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 Miami 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 792 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 Miami 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
Population112,63425th of 88571st of 3,144
Land area406.6 sq mi70th of 882,491st of 3,144
Population density277 per sq mi22nd of 88467th of 3,144
Median household income$76,81716th of 88734th of 3,143

Full data for Miami County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population112,634Vintage 2025 Population Estimates
Population in 2020108,974Vintage 2025 Population Estimates
2020 estimates base?108,781Vintage 2025 Population Estimates
Land area406.6 sq mi2025 Gazetteer Files
Water area3.1 sq mi2025 Gazetteer Files
Total area409.6 sq mi2025 Gazetteer Files
Population density?277 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$76,817American Community Survey 2020-2024 5-Year Estimates
Median home value$229,100American Community Survey 2020-2024 5-Year Estimates
Median age41.3American Community Survey 2020-2024 5-Year Estimates
Households44,906American Community Survey 2020-2024 5-Year Estimates
Housing units47,226American 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
-73
1,121 births, 1,194 deaths
Net migration
+840
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 5 areas bordering Miami 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
Montgomery CountyOhio23 mi539,598
Shelby CountyOhio22 mi48,065
Darke CountyOhio19 mi51,520
Clark CountyOhio11 mi135,340
Champaign CountyOhio9.9 mi38,820

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.