| County: | Lake County |
| State: | South Dakota |
| Ex Image: | Lake County Court House, Madison, South Dakota (75660).jpg |
| Ex Image Cap: | Lake County Court House |
| Founded Year: | 1873 |
| Seat Wl: | Madison |
| Largest City Wl: | Madison |
| Area Total Sq Mi: | 575 |
| Area Land Sq Mi: | 563 |
| Area Water Sq Mi: | 12 |
| Area Percentage: | 2.1 |
| Population As Of: | 2020 |
| Population Total: | 11059 |
| Pop Est As Of: | 2023 |
| Population Est: | 11031 |
| Population Density Sq Mi: | auto |
| Time Zone: | Central |
| Web: | http://www.lake.sd.gov/ |
| District: | At-large |
Lake County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 11,059.[1] Its county seat is Madison.[2] The county was formed in 1873.[3]
The terrain of Lake County consists of rolling hills, with the area devoted to agriculture. A tributary of the East Fork Vermillion River flows south-southeastward through the lower western part of the county, and Buffalo Creek flows southeastward from the central part of the county, leaving the county near its southeast corner.[4] The terrain generally slopes to the south, although high points (ca. 1,814' ASL) are found on the north and south boundary lines and points between.[5]
Lake County has a total area of, of which is land and (2.1%) is water.[6]
As of the 2020 census, there were 11,059 people, 4,576 households, and 2,804 families residing in the county.[7] The population density was . There were 5,658 housing units.
As of the 2010 census, there were 11,200 people, 4,483 households, and 2,814 families in the county. The population density was . There were 5,559 housing units at an average density of 9.9/mi2. The racial makeup of the county was 96.2% white, 0.7% Asian, 0.7% American Indian, 0.5% black or African American, 0.8% from other races, and 1.1% from two or more races. Those of Hispanic or Latino origin made up 1.6% of the population. In terms of ancestry, 50.7% were German, 20.6% were Norwegian, 12.4% were Irish, 6.6% were English, 6.2% were Dutch, 5.0% were Danish, and 5.0% were American.
Of the 4,483 households, 26.7% had children under the age of 18 living with them, 53.0% were married couples living together, 6.8% had a female householder with no husband present, 37.2% were non-families, and 30.9% of all households were made up of individuals. The average household size was 2.30 and the average family size was 2.88. The median age was 39.9 years.
The median income for a household in the county was $45,606 and the median income for a family was $57,753. Males had a median income of $36,370 versus $25,898 for females. The per capita income for the county was $22,447. About 6.5% of families and 12.1% of the population were below the poverty line, including 12.8% of those under age 18 and 8.8% of those age 65 or over.
Lake County voters have voted for Republican Party candidates in 62 percent of national elections since 1964.