| County: | Johnson County |
| State: | Iowa |
| Ex Image: | Johnson county courhouse iowa.jpg |
| Ex Image Size: | 240px |
| Seal: | Johnson County IA logo.jpg |
| Founded Date: | December 21 |
| Founded Year: | 1837 |
| Seat Wl: | Iowa City |
| Largest City Wl: | Iowa City |
| Area Total Sq Mi: | 623 |
| Area Land Sq Mi: | 614 |
| Area Water Sq Mi: | 9.1 |
| Area Percentage: | 1.5 |
| Census Yr: | 2020 |
| Pop: | 152854 |
| Pop Est As Of: | 2023 |
| Population Est: | 157528 |
| Pop Est Footnotes: | [1] |
| Density Sq Mi: | 250 |
| Time Zone: | Central |
| Web: | https://www.johnsoncountyiowa.gov/ |
| District: | 1st |
| Named For: | Richard Mentor Johnson (1837–2020) Lulu Johnson (since 2020) |
Johnson County is located in the U.S. state of Iowa. As of the 2020 census, the population was 152,854,[2] making it the fourth-most populous county in Iowa. The county seat is Iowa City,[3] 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.[4]
Johnson County was established in December 1837 by the legislature of the Wisconsin Territory, one of thirteen counties established by that body in a comprehensive act.[5] The county's area was partitioned from Dubuque County, and was not initially provided with a civil government, instead being governed by Cedar County officials. It was originally named for the US Vice President Richard M. Johnson (1780–1850).[6] In 2020, the Johnson County Board of Supervisors voted unanimously to change the county's namesake to be Lulu Merle Johnson (1907–1995), the first black woman in the state to earn a doctorate; Vice President Johnson was a slaveowner who had sexual relations with several of his slaves.[7]
The first courthouse in the county was a two-story log cabin structure, built in 1838 in the settlement of Napoleon,[8] about two miles south of the current courthouse.[9] The building stood across from what later would become the James McCollister Farmstead on land later owned by Philip Clark.
After Iowa City was established by fiat as the new territorial capitol of Iowa, the county seat was removed there.[10] 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.[9] This location was in the southeast corner of the intersection of Harrison and Clinton Streets. The building was 56 x 28 feet and two stories tall.[11] It was built by James Trimble, who had previously built the first jail.[9]
A third courthouse was built in 1857 in the courthouse square on Clinton Street between Court and Harrison Streets. It was used until 1901, after cracks appeared in its south wall in 1899.[12] The building was apparently built of brick with stone and wood ornamentation.[13]
The Richardsonian Romanesque style courthouse in use today was designed by the firm of Rush, Bowman and Rush of Grand Rapids, Michigan.[14] It was bid at a cost of $111,000 and built by the firm Rowson & Son of Johnson County.[15] The cornerstone was laid in December 1899.[16] The building's tower was based on Henry Hobson Richardson's design for the spire of Trinity Church in Boston.[17] The building was dedicated on June 8, 1901.[18] The currently unused jail that stands to the west of the courthouse was designed by C.L. Wundt of Burlington, Iowa on behalf of the Stewart Iron Works in Cleveland and bid for $14,000.[19]
According to the U.S. Census Bureau, the county has a total area of, of which is land and (1.5%) is water.[20]
The 2020 census recorded a population of 152,854 in the county, with a population density of . 93.62% of the population reported being of one race. There were 65,916 housing units, of which 61,335 were occupied.[2]
| White (NH) | 114,491 | 74.9% | |
| Black or African American (NH) | 12,643 | 8.3% | |
| Native American (NH) | 193 | 0.12% | |
| Asian (NH) | 8,555 | 5.6% | |
| Pacific Islander (NH) | 41 | 0.03% | |
| Other/Mixed (NH) | 6,733 | 4.4% | |
| Hispanic or Latino | 10,198 | 6.7% |
The 2010 census recorded a population of 130,882 in the county, with a population density of . There were 55,967 housing units, of which 52,715 were occupied.[22]
As of the census[23] of 2000, there were 111,006 people, 44,080 households, and 23,582 families residing in the county. The population density was 181sp=usNaNsp=us. There were 45,831 housing units at an average density of 75/mi2. 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.
Largely due to the presence of the University of Iowa, Johnson County is considered the most liberal county in Iowa and a stronghold of the Democratic Party, and has always been among Iowa's most Democratic counties since the Civil War. It has been the strongest Democratic county in the state since 1984. This trend predates the recent swing toward the Democrats in counties influenced by college towns. The last Republican to win the county in a presidential election was Richard Nixon in 1960, and the last Republican to even get 40 percent of the county's vote was Ronald Reagan in 1984. The last time the GOP won the county in a gubernatorial election was the 1978 Iowa gubernatorial election. As a measure of how strongly Democratic the county has been, Democrats easily carried it even in the national Republican landslides of 1972, 1984 and 1988, and the county was the only county in Iowa to vote for Democrat Alton B. Parker over Republican Theodore Roosevelt in 1904. In 2020, Joe Biden received the highest percentage of the vote received by any Democrat in the county's history; indeed, by any candidate of any party.[24] In 2024, it was the only county to not vote for Donald Trump in the state's Republican presidential caucuses. Nikki Haley won the county by a single vote.[25] [26] [27]
Johnson County's Democratic bent is just as pronounced at the state level. It was the lone county to vote Democratic in statewide Republican landslides, such as Senator Chuck Grassley's re-elections in 2010 and 2016 or Governor Terry Branstad's re-election in 2014.
The population ranking of the following table is based on the 2020 census of Johnson County.[2]
† county seat
| Rank | City/Town/etc. | Municipal type | Population (2020 Census) | |
|---|---|---|---|---|
| 1 | † Iowa City | City | 74,828 | |
| 2 | Coralville | City | 22,318 | |
| 3 | North Liberty | City | 20,479 | |
| 4 | Tiffin | City | 4,512 | |
| 5 | Solon | City | 3,018 | |
| 6 | West Branch (mostly in Cedar County) | City | 2,509 | |
| 7 | Lone Tree | City | 1,357 | |
| 8 | University Heights | City | 1,228 | |
| 9 | Swisher | City | 914 | |
| 10 | Hills | City | 863 | |
| 11 | Shueyville | City | 731 | |
| 12 | Oxford | City | 722 | |
| 13 | Frytown | CDP | 193 |