Adjacent counties

Major highways

• South Dakota Highway 19
• South Dakota Highway 46
• South Dakota Highway 50

Protected areas

• Missouri National Recreational River (part)
• Spirit Mound State Historic Prairie

2020 census

As of the 2020 census, there were 14,967 people, 5,564 households, and 2,795 families residing in the county.^[13] The population density was 36.3 inhabitants per square mile (14.0/km²). There were 6,180 housing units.

2010 census

As of the 2010 census, there were 13,864 people, 5,110 households, and 2,628 families in the county. The population density was 33.6 inhabitants per square mile (13.0/km²). There were 5,639 housing units at an average density of 13.7 per square mile (5.3/km²). The racial makeup of the county was 91.1% White, 3.1% American Indian, 1.7% Asian, 1.3% black or African American, 0.5% from other races, and 2.3% from two or more races. Those of Hispanic or Latino origin made up 2.0% of the population. In terms of ancestry, 43.9% were German, 16.4% were Norwegian, 15.8% were Irish, 8.7% were English, 5.4% were Swedish, and 1.8% were American.

Of the 5,110 households, 24.7% had children under the age of 18 living with them, 40.9% were married couples living together, 7.3% had a female householder with no husband present, 48.6% were non-families, and 32.4% of all households were made up of individuals. The average household size was 2.28 and the average family size was 2.91. The median age was 25.0 years.

The median income for a household in the county was $37,198 and the median income for a family was $61,159. Males had a median income of $37,059 versus $28,016 for females. The per capita income for the county was $19,518. About 8.0% of families and 24.0% of the population were below the poverty line, including 13.6% of those under age 18 and 6.7% of those age 65 or over.

Racial/ethnic makeup

The racial makeup of the county was 92.78% White, 1.00% Black or African American, 2.66% Native American, 1.95% Asian, 0.01% Pacific Islander, 0.29% from other races, and 1.31% from two or more races. 0.89% of the population were Hispanic or Latino of any race. 32.0% were of German, 15.6% Norwegian, 9.9% Irish and 5.4% English ancestry.

Religion

From 2000 Census data, over 50% consider themselves "unclaimed".^[14]

• Mainline Protestant with 3,840 is most common around 28%; mainly Lutheran;
• Catholic with 1820 comes second around 13%;
• Evangelical Protestant with 613 would be around 5%; mainly Lutheran Church–Missouri Synod and Southern Baptist.

Cities

• Irene (partial)
• Vermillion (county seat)

Town

• Wakonda

Census-designated places

• Burbank
• Meckling

Unincorporated communities

Townships