Jefferson County, Kansas

Jefferson County
Jefferson County Courthouse in Oskaloosa (1971)
Location within the U.S. state of Kansas
Kansas's location within the U.S.
Coordinates: 39°13′N 95°24′W / 39.217°N 95.400°W / 39.217; -95.400
Country United States
State Kansas
FoundedAugust 25, 1855
Named afterThomas Jefferson
SeatOskaloosa
Largest cityOskaloosa
Area
  Total
557 sq mi (1,440 km2)
  Land533 sq mi (1,380 km2)
  Water24 sq mi (60 km2)  4.3%
Population
 (2020)
  Total
18,368
  Estimate 
(2023)
18,327
  Density33/sq mi (13/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional district1st
Websitejfcountyks.com

Jefferson County is a county located in the U.S. state of Kansas. Its county seat and most populous city is Oskaloosa. As of the 2020 census, the county population was 18,368. The county was named after Thomas Jefferson, the 3rd president of the United States.