County Maps US

Montgomery County, Ohio

A county in Ohio, ranked 4 of 88 by population.

CountyFIPS 39113

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

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Population
539,598
+2,483 (+0.5%) since 2020
Land area
461.4
square miles. A further 0.6% of the total area is water
Population density
1,170
people per square mile, computed rather than published
County seat
Dayton
Seat of county government.
Established
1803
222 years ago
Largest city
Dayton city
Population 136,688 for the whole place, which extends beyond this county.

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 Montgomery 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 Montgomery 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 778 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 Montgomery 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
Population539,5984th of 88136th of 3,144
Land area461.4 sq mi37th of 882,224th of 3,144
Population density1,170 per sq mi6th of 88137th of 3,144
Median household income$66,13947th of 881,522nd of 3,143

Full data for Montgomery County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population539,598Vintage 2025 Population Estimates
Population in 2020537,115Vintage 2025 Population Estimates
2020 estimates base?537,304Vintage 2025 Population Estimates
Land area461.4 sq mi2025 Gazetteer Files
Water area2.9 sq mi2025 Gazetteer Files
Total area464.2 sq mi2025 Gazetteer Files
Population density?1,170 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$66,139American Community Survey 2020-2024 5-Year Estimates
Median home value$180,900American Community Survey 2020-2024 5-Year Estimates
Median age38.8American Community Survey 2020-2024 5-Year Estimates
Households231,319American Community Survey 2020-2024 5-Year Estimates
Housing units252,843American 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
-242
6,114 births, 6,356 deaths
Net migration
+2,883
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 7 areas bordering Montgomery 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
Miami CountyOhio23 mi112,634
Preble CountyOhio23 mi40,664
Greene CountyOhio21 mi174,322
Warren CountyOhio13 mi257,181
Butler CountyOhio6.1 mi400,128
Darke CountyOhio3.2 mi51,520
Clark CountyOhio2.0 mi135,340

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

Side by side

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.