Major highways

• Iowa Highway 5
• Iowa Highway 14
• Iowa Highway 92
• Iowa Highway 163
• Iowa Highway 316

Adjacent counties

• Jasper County (north)
• Mahaska County (east)
• Monroe County (southeast)
• Lucas County (southwest)
• Warren County (west)

2020 census

The 2020 census recorded a population of 33,414 in the county, with a population density of 58.4743/sq mi (22.5770/km²). 96.24% of the population reported being of one race. 91.15% were non-Hispanic White, 0.87% were Black, 2.09% were Hispanic, 0.21% were Native American, 1.20% were Asian, 0.06% were Native Hawaiian or Pacific Islander and 4.41% were some other race or more than one race. There were 14,073 housing units, of which 13,145 were occupied.^[1]

2010 census

The 2010 census recorded a population of 33,309 in the county, with a population density of 60.1018/sq mi (23.2054/km²). There were 13,914 housing units, of which 12,723 were occupied.^[11]

2000 census

As of the census^[12] of 2000, there were 32,052 people, 12,017 households, and 8,532 families residing in the county. The population density was 58 people per square mile (22 people/km²). There were 12,755 housing units at an average density of 23 units per square mile (8.9 units/km²). The racial makeup of the county was 97.46% White, 0.42% Black or African American, 0.19% Native American, 1.03% Asian, 0.04% Pacific Islander, 0.22% from other races, and 0.64% from two or more races. 0.80% of the population were Hispanic or Latino of any race.

There were 12,017 households, out of which 33.00% had children under the age of 18 living with them, 61.20% were married couples living together, 6.90% had a female householder with no husband present, and 29.00% were non-families. 25.60% of all households were made up of individuals, and 11.90% 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 3.02.

In the county, the population was spread out, with 25.30% under the age of 18, 10.20% from 18 to 24, 26.50% from 25 to 44, 22.10% from 45 to 64, and 15.90% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 98.60 males. For every 100 females age 18 and over, there were 95.80 males.

The median income for a household in the county was $42,401, and the median income for a family was $50,052. Males had a median income of $36,460 versus $25,573 for females. The per capita income for the county was $18,717. About 5.20% of families and 7.60% of the population were below the poverty line, including 8.70% of those under age 18 and 10.80% of those age 65 or over.

Cities

Unincorporated communities

Townships

Population ranking

The population ranking of the following table is based on the 2020 census of Marion County.^[1]

† county seat