Iowa County is a county in the U.S. state of Iowa. As of the 2020 census, the population was 16,662, and was estimated to be 16,423 in 2024. The county seat is Marengo and the largest city is Williamsburg. Iowa County is one of seven counties in the United States to share the same name as the state in which they are located. The other six counties are Arkansas County, Hawaii County, Idaho County, New York County, Oklahoma County, and Utah County.
Iowa County was formed on February 17, 1843. It was named for the Iowa River, which flows through the county. The first courthouse was a log cabin built in 1847. It was rented by the county until 1850 when a second courthouse was completed. In 1861 construction of a third courthouse was begun. The current courthouse was built in 1892 after the county had outgrown the previous one.
Iowa County is home to the Amana Colonies, a group of settlements of German Pietists comprising seven villages. Calling themselves the Ebenezer Society or the Community of True Inspiration (German: die Gemeinde der wahren Inspiration), they first settled in New York state near Buffalo in what is now West Seneca. However, in order to live out their beliefs in more isolated surroundings they moved west, to Iowa County in 1855, living a communal life until the mid-1930s. Today, Amana is a major tourist attraction known mainly for its restaurants and craft shops, and the colonies as a whole have been listed as a National Historic Landmark since 1965.
According to the United States Census Bureau, the county has a total area of , of which is land and (0.18%) is water. It is the 26th largest county in Iowa by total area. The county is intersected by the Iowa River and the north fork of the English River.
As of the second quarter of 2025, the median home value in Iowa County was $213,544.
As of the 2024 American Community Survey, there are 6,909 estimated households in Iowa County with an average of 2.34 persons per household. The county has a median household income of $71,223. Approximately 8.9% of the county's population lives at or below the poverty line. Iowa County has an estimated 65.3% employment rate, with 24.8% of the population holding a bachelor's degree or higher and 95.5% holding a high school diploma. There were 7,369 housing units at an average density of .
The top five reported languages (people were allowed to report up to two languages, thus the figures will generally add to more than 100%) were English (97.3%), Spanish (1.4%), Indo-European (0.7%), Asian and Pacific Islander (0.5%), and Other (0.1%).
The median age in the county was 42.4 years.
As of the 2020 census, there were 16,662 people, 6,811 households, and 4,509 families residing in the county. The population density was . There were 7,341 housing units at an average density of . The racial makeup of the county was 93.45% White, 0.67% African American, 0.21% Native American, 0.56% Asian, 0.01% Pacific Islander, 1.34% from some other races and 3.76% from two or more races. Hispanic or Latino people of any race were 2.97% of the population.
And 96.24% of residents reported being of one race. The median age was 42.6 years; 23.4% of residents were under the age of 18 and 19.8% were 65 years of age or older. For every 100 females there were 98.8 males, and for every 100 females age 18 and over there were 95.9 males age 18 and over.
<0.1% of residents lived in urban areas, while 100.0% lived in rural areas.
There were 6,811 households in the county, of which 28.9% had children under the age of 18 living in them. Of all households, 55.3% were married-couple households, 16.9% were households with a male householder and no spouse or partner present, and 21.6% were households with a female householder and no spouse or partner present. About 28.7% of all households were made up of individuals and 13.7% had someone living alone who was 65 years of age or older.
There were 7,341 housing units, of which 6,811 were occupied; 7.2% were vacant. Among occupied housing units, 79.1% were owner-occupied and 20.9% were renter-occupied. The homeowner vacancy rate was 1.5% and the rental vacancy rate was 8.6%.
As of the 2010 census, there were 16,355 people, 6,677 households, and _ families residing in the county. The population density was . There were 7,258 housing units at an average density of . The racial makeup of the county was 97.84% White, 0.35% African American, 0.17% Native American, 0.34% Asian, 0.01% Pacific Islander, 0.54% from some other races and 0.75% from two or more races. Hispanic or Latino people of any race were 1.88% of the population.
As of the 2000 census, there were 15,671 people, 6,163 households, and 4,301 families residing in the county. The population density was . There were 6,545 housing units at an average density of . The racial makeup of the county was 98.70% White, 0.17% African American, 0.06% Native American, 0.30% Asian, 0.03% Pacific Islander, 0.36% from some other races and 0.38% from two or more races. Hispanic or Latino people of any race were 0.97% of the population.
There were 6,163 households, out of which 32.80% had children under the age of 18 living with them, 60.10% were married couples living together, 6.60% had a female householder with no husband present, and 30.20% were non-families. 25.90% of all households were made up of individuals, and 12.50% had someone living alone who was 65 years of age or older. The average household size was 2.50 and the average family size was 3.03. In the county the population was spread out, with 26.40% under the age of 18, 6.30% from 18 to 24, 27.80% from 25 to 44, 22.40% from 45 to 64, and 17.10% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 95.00 males. For every 100 females age 18 and over, there were 93.20 males.
The median income for a household in the county was $41,222, and the median income for a family was $48,946. Males had a median income of $31,220 versus $24,652 for females. The per capita income for the county was $18,884. About 3.40% of families and 5.00% of the population were below the poverty line, including 4.50% of those under age 18 and 5.40% of those age 65 or over.
In the 2008 US presidential election, a nearly equal number of Iowa County voters voted for each major candidate, with Barack Obama winning the county by a narrow margin of 14 votes.
In the 2012 US presidential election, Mitt Romney received 4,551 votes (51.8%). In the 2016 US presidential election, Donald Trump received 5,193 votes (59.1%). In the 2020 US presidential election, Donald Trump received 6,009 votes (61.8%). In the 2024 US presidential election, Donald Trump received 6,068 votes (63.0%).
Population rankings based on the 2020 census of Iowa County:
â county seat
School districts include: