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Johnson County, Iowa facts for kids

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Johnson County
County Courthouse
Official seal of Johnson County
Map of Iowa highlighting Johnson County
Location within the U.S. state of Iowa
Map of the United States highlighting Iowa
Iowa's location within the U.S.
Country  United States
State  Iowa
Founded 1837
Named for Richard Mentor Johnson
Seat Iowa City
Largest city Iowa City
 • Total 623 sq mi (1,610 km2)
 • Land 614 sq mi (1,590 km2)
 • Water 9.1 sq mi (24 km2)  1.5%%
 • Total 130,882
 • Density 213/sq mi (82/km2)
Time zone UTC−6 (Central)
 • Summer (DST) UTC−5 (CDT)
Congressional district 2nd

Johnson County is a county located in the U.S. state of Iowa. As of the 2010 census, the population was 130,882 making it the fifth-most populous county in Iowa. The county seat is Iowa City, home of the University of Iowa. The county is named for Richard Mentor Johnson, the ninth vice president of the United States.

Johnson County is included in the Iowa City, IA Metropolitan Statistical Area, which is also included in the Cedar Rapids-Iowa City Corridor Combined Statistical Area.


Johnson County was created on December 21, 1837 by the legislature of the Wisconsin Territory. The county was carved out of territory formerly in Dubuque County, and was not initially provided with a civil government, instead being governed by Cedar County officials. It was named for the US Vice President Richard M. Johnson.

The first courthouse in the county was a two story log cabin structure, built in 1838 in the town of Napoleon, about two miles south of the current courthouse. The building stood across from what later would become the James McCollister Farmstead on land later owned by Philip Clark.

Old Johnson Cty Courthouse
Old Johnson County Courthouse, Iowa City, 1857-1899

After Iowa City was established by fiat as the new territorial capitol of Iowa, the county seat was removed there. The second Johnson County Courthouse, the first in Iowa City, was built on Lot 8 Block 8 of the County Seat Addition to Iowa City in 1842 for $3,690. This location was in the southeast corner of the intersection of Harrison and Clinton Streets. The building was intended to be 56 x 28 feet and two stories tall. The building was built by James Trimble, who had previously built the first jail.

A third courthouse was built in 1857 in the courthouse square located on Clinton Street between Court and Harrison Streets. It was used until it was found to be dangerous due to cracks in the south wall in 1899. The building was apparently built of brick with stone and wood ornamentation.

The Richardsonian Romanesque style courthouse in use today was designed by the firm of Rush, Bowman and Rush of Grand Rapids, MI. It was bid at a cost of $111,000 and built by the firm Rowson and Son of Johnson County. The cornerstone was laid in December 1899. The building's tower was based on Henry Hobson Richardson's design for the spire of Trinity Church in Boston. The building was dedicated on June 8, 1901. The currently unused jail that stands to the west of the courthouse was designed by C.L. Wundt of Burlington on behalf of the Stewart Iron Works, Cleveland, OH and bid for $14,000.


According to the U.S. Census Bureau, the county has a total area of 623 square miles (1,610 km2), of which 614 square miles (1,590 km2) is land and 9.1 square miles (24 km2) (1.5%) is water.

Major highways

  • I-80.svg Interstate 80
  • I-380 (IA).svg Interstate 380
  • US 6.svg U.S. Highway 6
  • US 218 (IA).svg U.S. Highway 218
  • Iowa 1.svg Iowa Highway 1
  • Iowa 22.svg Iowa Highway 22
  • Iowa 27.svg Iowa Highway 27

Adjacent counties


Historical population
Census Pop.
1850 4,472
1860 17,573 293.0%
1870 24,898 41.7%
1880 25,429 2.1%
1890 23,082 −9.2%
1900 24,817 7.5%
1910 25,914 4.4%
1920 26,462 2.1%
1930 30,276 14.4%
1940 33,191 9.6%
1950 45,756 37.9%
1960 53,663 17.3%
1970 72,127 34.4%
1980 81,717 13.3%
1990 96,119 17.6%
2000 111,006 15.5%
2010 130,882 17.9%
Est. 2015 144,251 10.2%
U.S. Decennial Census
1790-1960 1900-1990
1990-2000 2010-2013

2010 census

The 2010 census recorded a population of 130,882 in the county, with a population density of 212.9964/sq mi (82.2384/km2). There were 55,967 housing units, of which 52,715 were occupied.

2000 census

USA Johnson County, Iowa age pyramid
2000 Census Age Pyramid for Johnson County

As of the census of 2000, there were 111,006 people, 44,080 households, and 23,582 families residing in the county. The population density was 181 people per square mile (70/km²). There were 45,831 housing units at an average density of 75 per square mile (29/km²). The racial makeup of the county was 90.13% White, 2.90% Black or African American, 0.28% Native American, 4.12% Asian, 0.04% Pacific Islander, 1.01% from other races, and 1.51% from two or more races. 2.51% of the population were Hispanic or Latino of any race.

There were 44,080 households out of which 26.50% had children under the age of 18 living with them, 43.90% were married couples living together, 6.80% had a female householder with no husband present, and 46.50% were non-families. 30.20% of all households were made up of individuals and 5.60% had someone living alone who was 65 years of age or older. The average household size was 2.34 and the average family size was 2.97.

Age spread: 20.10% under the age of 18, 23.40% from 18 to 24, 30.80% from 25 to 44, 18.20% from 45 to 64, and 7.40% who were 65 years of age or older. The median age was 28 years. For every 100 females there were 99.10 males. For every 100 females age 18 and over, there were 97.30 males.

The median income for a household in the county was $40,060, and the median income for a family was $60,112. Males had a median income of $36,279 versus $29,793 for females. The per capita income for the county was $22,220. About 5.20% of families and 15.00% of the population were below the poverty line, including 8.10% of those under age 18 and 3.80% of those age 65 or over.



Census-designated place

Other unincorporated communities

Ghost towns


  • Big Grove Township
  • Cedar Township
  • Clear Creek Township
  • East Lucas Township
  • Fremont Township
  • Graham Township
  • Hardin Township
  • Jefferson Township
  • Liberty Township
  • Lincoln Township
  • Madison Township
  • Monroe Township
  • Newport Township
  • Oxford Township
  • Penn Township
  • Pleasant Valley Township
  • Scott Township
  • Sharon Township
  • Union Township
  • Washington Township

Population ranking

The population ranking of the following table is based on the 2010 census of Johnson County.

county seat

Rank City/Town/etc. Municipal type Population (2010 Census)
1 Iowa City City 67,862
2 Coralville City 18,907
3 North Liberty City 13,374
4 West Branch (mostly in Cedar County) City 2,322
5 Solon City 2,037
6 Tiffin City 1,947
7 Lone Tree City 1,300
8 University Heights City 1,051
9 Swisher City 879
10 Oxford City 807
11 Hills City 703
12 Shueyville City 577
13 Frytown CDP 165

Notable natives

  • John T. Struble (1831–1916) early builder and farmer.
  • Grant Wood, painter.
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