Johnson County, Iowa

Johnson County, Iowa
The Johnson County Courthouse in Iowa City
Location within the U.S. state of Iowa
Coordinates: 41°40′14″N 91°35′26″W / 41.670668°N 91.590529°W / 41.670668; -91.590529
Country United States
State Iowa
FoundedDecember 21, 1837 (created)
July 4, 1838 (organized)
Named afterRichard Mentor Johnson (1837–2020)
Lulu Johnson (since 2020)
SeatIowa City
Largest cityIowa City
Area
 • Total
623.063 sq mi (1,613.73 km2)
 • Land612.997 sq mi (1,587.65 km2)
 • Water10.066 sq mi (26.07 km2)  1.62%
Population
 (2020)
 • Total
152,854
 • Estimate 
(2024)
160,080
 • Density249.355/sq mi (96.2766/km2)
Time zoneUTC−6 (Central)
 • Summer (DST)UTC−5 (CDT)
Area code319
Congressional district1st
Websitejohnsoncountyiowa.gov
  • Iowa county number 52

Johnson County is located in the U.S. state of Iowa. As of the 2020 census, the population was 152,854, and was estimated to be 160,080 in 2024, making it the fourth-most populous county in Iowa. The county seat and the largest city is Iowa City, home of the University of Iowa. Johnson County is included in the Iowa City metropolitan area, which is also included in the Cedar Rapids-Iowa City Corridor Combined Statistical Area.