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County · code 19123

Mahaska CountyIowa

Mahaska County is in Iowa, with its seat in Oskaloosa. The county was created on February 17, 1843, from parts of Keokuk and Washington counties and named after Mahaska.

  • Founded1843
  • County seatOskaloosa
  • Named forMahaska
  • Land area571 sq mi + 2.6 sq mi water
  • Population22,190 2020 Census
  • Parcels mapped22,498 checked 14 October 2026
Open the free map Click any parcel in Mahaska County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

MarionKeokuk Oskaloosa Census outline · seat marked

Where it is

Mahaska on the map of Iowa

Iowa has 99 counties and county equivalents, each with its own records office. Shapes with a page are links.

Adair CountyAdams CountyAllamakee CountyAppanoose CountyAudubon CountyBenton CountyBlack Hawk CountyBoone CountyBremer CountyBuchanan CountyBuena Vista CountyButler CountyCalhoun CountyCarroll CountyCass CountyCedar CountyCerro Gordo CountyCherokee CountyChickasaw CountyClarke CountyClay CountyClayton CountyClinton CountyCrawford CountyDallas CountyDavis CountyDecatur CountyDelaware CountyDes Moines CountyDickinson CountyDubuque CountyEmmet CountyFayette CountyFloyd CountyFranklin CountyFremont CountyGreene CountyGrundy CountyGuthrie CountyHamilton CountyHancock CountyHardin CountyHarrison CountyHenry CountyHoward CountyHumboldt CountyIda CountyIowa CountyJackson CountyJasper CountyJefferson CountyJohnson CountyJones CountyKeokuk CountyKossuth CountyLee CountyLinn CountyLouisa CountyLucas CountyLyon CountyMadison CountyMarion CountyMarshall CountyMills CountyMitchell CountyMonona CountyMonroe CountyMontgomery CountyMuscatine CountyO'Brien CountyOsceola CountyPage CountyPalo Alto CountyPlymouth CountyPocahontas CountyPolk CountyPottawattamie CountyPoweshiek CountyRinggold CountySac CountyScott CountyShelby CountySioux CountyStory CountyTama CountyTaylor CountyUnion CountyVan Buren CountyWapello CountyWarren CountyWashington CountyWayne CountyWebster CountyWinnebago CountyWinneshiek CountyWoodbury CountyWorth CountyWright CountyMahaska County Mahaska
Counties of Iowa · Mahaska highlighted

History

Formed in 1843 from Keokuk County and Washington County

An old deed may name a county that no longer exists, or a boundary that has since moved.

Mahaska County was created by Iowa Territory from Keokuk and Washington counties on February 17, 1843, initially unorganized and attached to Washington for judicial, revenue, and election purposes. The county became fully organized on March 1, 1844, detached from Washington, and received additional attached non-county areas for administrative purposes. Between 1845 and 1851, Mahaska lost substantial attached territory to the creation of Marion, Madison, Warren, Dallas, Jasper, Polk, Pottawattamie, and Adair counties. Mahaska became an official Iowa county on December 28, 1846, when Iowa achieved statehood.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries; the 5 that matter most are shown first.

  1. 1843
    Mahaska County created Mahaska created by Iowa Territory from Keokuk and Non-County Area 3 attached to Washington; Mahaska not fully organized, attached to Washington "for judicial, revenue, and election purposes."
    from Keokukfrom Washington
    · Iowa Terr. Rev. Stat. 1843, ch. 34, sec. 6/pp. 132-133
  2. 1845
    Lost territory Mahaska lost part of attached Non-County Area 3 to creation of Marion.
    to Marion
    · Iowa Terr. Laws 1845, ch. 57, sec. 1/pp. 93-96
  3. 1846
    Lost territory Mahaska lost part of attached Non-County Area 3 to creation of Madison and Warren; lost part of attached Non-County Area 8 to creation of Dallas, Jasper, and Polk.
    to Madisonto Warrento Dallasto Jasperto Polk
    · Iowa Terr. Laws 1845-1846, ch. 82, secs. 3-4, 6, 9-10/pp. 74-75
  4. 1846
    Lost territory Mahaska lost part of attached Non-County Area 8 to Dallas.
    to Dallas
    · Iowa Terr. Laws 1845-1846, ch. 83, secs. 1-3/pp. 75-76
  5. 1846
    Became part of Iowa Mahaska became an Iowa county when the state of Iowa was created from Iowa Territory. · U.S. Stat., vol. 9, ch. 1[1847]/p. 117
Show all 10 changes (5 more)
  1. 1843
    Mahaska County created Mahaska created by Iowa Territory from Keokuk and Non-County Area 3 attached to Washington; Mahaska not fully organized, attached to Washington "for judicial, revenue, and election purposes."
    from Keokukfrom Washington
    · Iowa Terr. Rev. Stat. 1843, ch. 34, sec. 6/pp. 132-133
  2. 1844
    Changed Mahaska fully organized, detached from Washington; Non-County Area 3 detached from Washington, attached to Mahaska "for election, revenue, and judicial purposes"; Poweshiek and Non-County Area 8 detached from Iowa, attached to Mahaska "for election, revenue, and judicial purposes."
    WashingtonPoweshiekIowa
    · Iowa Terr. Laws 1843-1844, ch. 68, secs.1, 17-18/pp. 85-89
  3. 1845
    Lost territory Mahaska lost part of attached Non-County Area 3 to creation of Marion.
    to Marion
    · Iowa Terr. Laws 1845, ch. 57, sec. 1/pp. 93-96
  4. 1846
    Lost territory Mahaska lost part of attached Non-County Area 3 to creation of Madison and Warren; lost part of attached Non-County Area 8 to creation of Dallas, Jasper, and Polk.
    to Madisonto Warrento Dallasto Jasperto Polk
    · Iowa Terr. Laws 1845-1846, ch. 82, secs. 3-4, 6, 9-10/pp. 74-75
  5. 1846
    Lost territory Mahaska lost part of attached Non-County Area 8 to Dallas.
    to Dallas
    · Iowa Terr. Laws 1845-1846, ch. 83, secs. 1-3/pp. 75-76
  6. 1846
    Changed Non-County Area 8 detached from Mahaska, became part of Non-County Area 9 attached to Polk "for election, revenue, and judicial purposes."
    Polk
    · Iowa Terr. Laws 1845-1846, ch. 101, secs. 1, 11-12/pp. 92-95
  7. 1846
    Became part of Iowa Mahaska became an Iowa county when the state of Iowa was created from Iowa Territory. · U.S. Stat., vol. 9, ch. 1[1847]/p. 117
  8. 1847
    Lost territory Mahaska lost most of attached Non-County Area 3 to creation of Pottawattamie.
    to Pottawattamie
    · Iowa Acts 1846-1847, ch. 84, sec. 1/pp. 100-101; Swisher, "Organization of Counties," 519-520
  9. 1848
    Changed Poweshiek fully organized, detached from Mahaska.
    Poweshiek
    · Iowa Acts 1848, ext. sess., ch. 54, sec. 1/pp. 55-57
  10. 1851
    Lost territory Mahaska lost all of attached Non-County Area 3 to Pottawattamie and to creation of Adair; Non-County Area 3 eliminated.
    to Pottawattamieto Adair
    · Iowa Acts 1850-1851, ch. 9, sec. 2/p. 27

Land and parcels

What the maps cover in Mahaska

Who publishes each layer, how good it is, and when we last checked.

Official
from the office that keeps the record
Good enough
a reliable statewide or national copy
Fallback
a guide only; check the official record
Missing
nothing public found yet

People and land

Mahaska by the Census

Population
22,190 2020 Census count
Housing units
9,680 2020 Census count
Land area
571 square miles
Water area
2.6 square miles
People per sq mi
39 population ÷ land area

Source: US Census Bureau, 2020 Census; US Census Bureau, 2020 Gazetteer Files. Not endorsed or certified by the Census Bureau.

Rules and offices

Who to ask before you build, dig or sell

Official county pages only. We link to them; we do not copy them, because they change.

Inside a city or town, permits usually come from that city rather than the county.

Permits

Zoning and code

County government

See your own lot on these maps

Open Mahaska County on Parcel Chart's free map and click your parcel. Save it with a free account; the full record of your place (site map, projects, documents) is Pro, in early access.

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Questions

Common questions about Mahaska County

When was Mahaska County founded?
Mahaska County was founded in 1843, formed from Keokuk County and Washington County, and named after Mahaska.
What is the county seat of Mahaska County?
The county seat of Mahaska County is Oskaloosa.
Is there an online parcel map for Mahaska County?
Yes. A public source publishes a parcel map of 22,498 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Mahaska County's boundary or name changed?
Mahaska County was created in 1843 from Keokuk County and Washington County. Since then the Atlas of Historical County Boundaries records 9 later changes, chiefly involving Dallas County, Polk County and Pottawattamie County.
Who issues building permits in Mahaska County?
The county's page on building permits: Weapon Permits. Inside a city or town, ask that city first.
Is my lot in a flood zone?
We do not have flood maps for Mahaska County yet. Look up the address on FEMA's Flood Map Service Center, which shows the effective flood map for any lot.

Nearby

Counties next door