According to the United States Census Bureau, the county has a total area of 573.199 square miles (1,484.58km2), of which 572.503 square miles (1,482.78km2) is land and 0.696 square miles (1.80km2) (0.12%) is water.[7] It is the 43rd largest county in Iowa by total area.[8]
As of the second quarter of 2025, the median home value in Marshall County was $150,876.[14]
As of the 2024 American Community Survey, there are 15,546 estimated households in Marshall County with an average of 2.48 persons per household. The county has a median household income of $72,785. Approximately 11.1% of the county's population lives at or below the poverty line. Marshall County has an estimated 63.9% employment rate, with 21.4% of the population holding a bachelor's degree or higher and 87.0% holding a high school diploma.[3] There were 16,860 housing units at an average density of 29.45 per square mile (11.4/km2).
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 (76.2%), Spanish (19.0%), Indo-European (0.5%), Asian and Pacific Islander (4.0%), and Other (0.3%).
The median age in the county was 38.7 years.
Marshall County, Iowa – racial and ethnic composition Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos may be of any race.
As of the 2020 census, there were 40,105 people, 15,358 households, and 10,161 families residing in the county.[20] The population density was 0.0 inhabitants per square mile (0.0/km2). There were 16,745 housing units at an average density of 29.25 per square mile (11.3/km2). The racial makeup of the county was 73.75% White, 2.03% African American, 0.82% Native American, 3.78% Asian, 0.08% Pacific Islander, 10.29% from some other races and 9.24% from two or more races. Hispanic or Latino people of any race were 22.79% of the population.[21]
2010 census
As of the 2010 census, there were 40,648 people, 15,538 households, and _ families residing in the county. The population density was 71.00 inhabitants per square mile (27.4/km2). There were 16,831 housing units at an average density of 29.40 per square mile (11.4/km2). The racial makeup of the county was 88.74% White, 1.67% African American, 0.46% Native American, 1.32% Asian, 0.12% Pacific Islander, 5.65% from some other races and 2.04% from two or more races. Hispanic or Latino people of any race were 17.26% of the population.
2000 census
As of the 2000 census, there were 39,311 people, 15,338 households, and 10,460 families residing in the county. The population density was 68.67 inhabitants per square mile (26.5/km2). There were 16,324 housing units at an average density of 28.51 per square mile (11.0/km2). The racial makeup of the county was 90.44% White, 0.93% African American, 0.35% Native American, 0.78% Asian, 0.06% Pacific Islander, 6.03% from some other races and 1.42% from two or more races. Hispanic or Latino people of any race were 8.96% of the population.
There were 15,338 households 31.10% had children under the age of 18 living with them, 55.40% were married couples living together, 9.30% had a female householder with no husband present, and 31.80% were non-families. 26.90% of households were one person and 12.20% were one person aged 65 or older. The average household size was 2.48 and the average family size was 3.00.
The age distribution was 25.30% under the age of 18, 8.10% from 18 to 24, 26.30% from 25 to 44, 23.90% from 45 to 64, and 16.40% 65 or older. The median age was 39 years. For every 100 females there were 99.20 males. For every 100 females age 18 and over, there were 96.50 males.
The median household income was $38,268 and the median family income was $46,627. Males had a median income of $33,809 versus $24,063 for females. The per capita income for the county was $19,176. About 7.10% of families and 10.20% of the population were below the poverty line, including 14.30% of those under age 18 and 8.60% of those age 65 or over.
Prior to 1964, Marshall County was strongly Republican, never backing a Democratic presidential candidate from 1880 to 1960 and only failing to back a Republican candidate during those years in 1912 with a strong third-party campaign by former president Theodore Roosevelt on the Bull Moose ticket. Since then, it has become far more of a swing county, having backed the national winner in the seven presidential elections from 1992 to 2016. That streak was broken in 2020, when Donald Trump won the county but lost nationally. The county is considered a bellwetherpolity.[23]
United States presidential election results for Marshall County, Iowa[24]
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