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County · code 20087

Jefferson CountyKansas

Jefferson County is a county in Kansas with its seat in Oskaloosa, formed in 1855.

  • Founded1855
  • County seatOskaloosa
  • Named forThomas Jefferson
  • Land area533 sq mi + 24 sq mi water
  • Population18,368 2020 Census
  • Parcels mapped15,515 checked 15 October 2026
Open the free map Click any parcel in Jefferson County: acreage, parcel id, address and who publishes the map. No sign-in.

Updated

AtchisonLeavenworthDouglasShawneeJackson Oskaloosa Census outline · seat marked

Where it is

Jefferson on the map of Kansas

Kansas has 105 counties and county equivalents, each with its own records office. Shapes with a page are links.

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Counties of Kansas · Jefferson highlighted

History

Founded in 1855

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

Jefferson County was created by Kansas Territory from non-county area on August 25, 1855. It became a county in the state of Kansas on January 29, 1861. The county lost territory to Douglas County in 1865 and had a boundary adjustment with Shawnee County in 1899.

Boundary changes from the Newberry Library, Atlas of Historical County Boundaries.

  1. 1855
    Jefferson County created Jefferson created by Kansas Territory from non-county area. · Kans. Terr. Laws 1855, 1st leg., ch. 30, sec. 29/pp. 209-210
  2. 1857
    Lost territory Jefferson lost to Calhoun (now Jackson).
    to Calhounto Jackson
    · Kans. Terr. Laws 1857, 2d leg., sec. 29/p. 44
  3. 1861
    Became part of Kansas Jefferson became a county in the state of Kansas. · U.S. Stat., vol. 12, ch. 20 [1861]/pp. 126-128; Van Zandt, 138-139
  4. 1865
    Lost territory Jefferson lost to Douglas.
    to Douglas
    · Kans. Laws 1865, 5th leg., ch. 14/p. 44
  5. 1899
    Changed Boundary between Jefferson and Shawnee in sections 23 and 26, township 11 south, range 16 east was adjusted to run on the Kansas River.
    Shawnee
    · Kans. Laws 1899, 28th leg., ch. 56/p. 121

Land and parcels

What the maps cover in Jefferson

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

Jefferson by the Census

Population
18,368 2020 Census count
Housing units
7,911 2020 Census count
Land area
533 square miles
Water area
24 square miles
People per sq mi
34 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.

Records

Permits

Zoning and code

County government

See your own lot on these maps

Open Jefferson 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 Jefferson County

When was Jefferson County founded?
Jefferson County was founded in 1855, and named after Thomas Jefferson.
What is the county seat of Jefferson County?
The county seat of Jefferson County is Oskaloosa.
Is there an online parcel map for Jefferson County?
Yes. A public source publishes a parcel map of 15,515 parcels, rated good enough here. You can click any parcel on it in Parcel Chart's free map, no sign-in needed.
Has Jefferson County's boundary or name changed?
Jefferson County was created in 1855. Since then the Atlas of Historical County Boundaries records 4 later changes, chiefly involving Calhoun County, Douglas County and Jackson County.
Who issues building permits in Jefferson County?
The county's page on building permits: Permits. Inside a city or town, ask that city first.
Who issues septic and well permits in Jefferson County?
The county's page on septic systems and wells: Health Dept. Staff Directory.
Is my lot in a flood zone?
We do not have flood maps for Jefferson 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