Johnson County, Kansas

Johnson County
Former Johnson County Courthouse in Olathe (2009). It was opened in 1952, closed in 2020, then demolished in 2021 after a new courthouse was finished.
Location within the U.S. state of Kansas
Kansas's location within the U.S.
Coordinates: 38°52′N 94°52′W / 38.867°N 94.867°W / 38.867; -94.867
Country United States
State Kansas
FoundedAugust 25, 1855
Named afterThomas Johnson
SeatOlathe
Largest cityOverland Park
Area
  Total
480 sq mi (1,200 km2)
  Land473 sq mi (1,230 km2)
  Water6.5 sq mi (17 km2)  1.4%
Population
 (2020)
  Total
609,863
  Estimate 
(2023)
622,237
  Density1,300/sq mi (490/km2)
Time zoneUTC−6 (Central)
  Summer (DST)UTC−5 (CDT)
Congressional district3rd
Websitejocogov.org

Johnson County is a county in the U.S. state of Kansas, along the border of the state of Missouri. Its county seat is Olathe. As of the 2020 census, the population was 609,863, making it the most populous county in Kansas. The county was named after Thomas Johnson, a Methodist missionary who was one of the state's first settlers. Largely suburban, the county contains a number of suburbs of Kansas City, Missouri, including Overland Park, a principal city of and the second most populous city in the Kansas City Metropolitan Area.