County Maps US

Mahaska County, Iowa

A county in Iowa, ranked 28 of 99 by population.

CountyFIPS 19123

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

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Population
21,880
-271 (-1.2%) since 2020
Land area
570.9
square miles. A further 0.4% of the total area is water
Population density
38.3
people per square mile, computed rather than published
County seat
Oskaloosa
Seat of county government.
Established
1843
182 years ago
Largest city
Oskaloosa city
Population 11,493.

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 Mahaska 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 Mahaska County, Iowa 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 796 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 Mahaska County ranks

Position among the 99 counties of Iowa, and among all 3,144 US counties and county-equivalents. Computed from the figures on this page.

MeasureValueIn IowaNationally
Population21,88028th of 991,726th of 3,144
Land area570.9 sq mi46th of 991,765th of 3,144
Population density38.3 per sq mi28th of 991,709th of 3,144
Median household income$70,94052nd of 991,131st of 3,143

Full data for Mahaska County

Every figure below is attributed to the Census Bureau product it came from, with the vintage of that product.
MeasureValueSource and vintage
Population21,880Vintage 2025 Population Estimates
Population in 202022,151Vintage 2025 Population Estimates
2020 estimates base?22,182Vintage 2025 Population Estimates
Land area570.9 sq mi2025 Gazetteer Files
Water area2.5 sq mi2025 Gazetteer Files
Total area573.4 sq mi2025 Gazetteer Files
Population density?38.3 per sq miComputed: Vintage 2025 estimates divided by 2025 Gazetteer land area
Median household income$70,940American Community Survey 2020-2024 5-Year Estimates
Median home value$157,800American Community Survey 2020-2024 5-Year Estimates
Median age39.0American Community Survey 2020-2024 5-Year Estimates
Households8,743American Community Survey 2020-2024 5-Year Estimates
Housing units9,728American 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
-24
237 births, 261 deaths
Net migration
-6
More people moved out than moved in.

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

The 6 areas bordering Mahaska 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
Keokuk CountyIowa24 mi9,797
Marion CountyIowa24 mi34,192
Poweshiek CountyIowa18 mi18,368
Wapello CountyIowa12 mi35,210
Monroe CountyIowa12 mi7,406
Jasper CountyIowa6.0 mi38,153

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

All 99 counties of Iowa

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

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