Codington County terrain consists of rolling hills dotted with lakes and ponds, especially in the SW portion. The land is largely devoted to agriculture. The terrain is higher on the county's east and west sides, and generally slopes to the south. The county has a total area of, of which is land and is water.
As of the 2000 United States Census, there were 25,897 people, 10,357 households, and 6,877 families in the county. The population density was 38 people per square mile. There were 11,324 housing units at an average density of 16 per square mile. The racial makeup of the county was 96.74% White, 0.14% Black or African American, 1.41% Native American, 0.28% Asian, 0.02% Pacific Islander, 0.57% from other races, and 0.84% from two or more races. 1.06% of the population were Hispanic or Latino of any race. 48.2% were of German, 20.0% Norwegian and 5.5% Irish ancestry, 96.7% spoke English, 1.5% Spanish and 1.2% German as their first language. There were 10,357 households out of which 33.60% had children under the age of 18 living with them, 54.50% were married couplesliving together, 8.10% had a female householder with no husband present, and 33.60% were non-families. 27.90% of all households were made up of individuals and 10.80% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 3.04. The county population contained 26.80% under the age of 18, 10.40% from 18 to 24, 28.00% from 25 to 44, 20.70% from 45 to 64, and 14.10% who were 65 years of age or older. The median age was 35 years. For every 100 females, there were 98.50 males. For every 100 females age 18 and over, there were 96.50 males. The median income for a household in the county was $36,257, and the median income for a family was $45,153. Males had a median income of $30,279 versus $19,826 for females. The per capita income for the county was $18,761. About 5.60% of families and 9.00% of the population were below the poverty line, including 8.60% of those under age 18 and 10.80% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 27,227 people, 11,432 households, and 7,216 families in the county. The population density was. There were 12,397 housing units at an average density of. The racial makeup of the county was 95.3% white, 2.0% American Indian, 0.4% Asian, 0.3% black or African American, 0.6% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 1.6% of the population. In terms of ancestry, 54.3% were German, 22.6% were Norwegian, 9.6% were Irish, 6.7% were English, and 3.3% were American. Of the 11,432 households, 30.7% had children under the age of 18 living with them, 49.9% were married couples living together, 9.0% had a female householder with no husband present, 36.9% were non-families, and 30.6% of all households were made up of individuals. The average household size was 2.35 and the average family size was 2.93. The median age was 37.7 years. The median income for a household in the county was $43,275 and the median income for a family was $60,202. Males had a median income of $39,076 versus $26,945 for females. The per capita income for the county was $24,781. About 8.9% of families and 12.7% of the population were below the poverty line, including 13.7% of those under age 18 and 16.8% of those age 65 or over.
Codington County voters have been reliably Republican for several decades. In no national election since 1976 has the county selected the Democratic Party candidate.
