Sully County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 1,446, making it the fifth-least populous county in South Dakota. Its county seat is Onida. The county was created in 1873 and organized in 1883. It is named after General Alfred Sully, who built Fort Sully. Sully County is included in the Micropolitan Statistical Area of Pierre.

Geography

The west boundary line of Sully County is defined by the meanderings of the Missouri River, which flows southward along its edge. The county's terrain is composed of semi-arid rolling hills, partially devoted to agriculture. The terrain slopes to the south and east, but the west portion of the county slopes westward into the river valley. The county's highest point is along the midpoint of its north boundary line, at 1,949 ft ASL. The county has a total area of 1070 sqmi, of which 1007 sqmi is land and 63 sqmi (5.9%) is water. The eastern portion of South Dakota's counties (48 of 66) observe Central Time; the western counties (18 of 66) observe Mountain Time. Sully County is at the western edge of those counties that observe Central Time.

Major highways

Adjacent counties

Protected areas

Lakes

Demographics

2020 census

As of the 2020 census, there were 1,446 people, 635 households, and 428 families residing in the county. The population density was 1.4 PD/sqmi. There were 892 housing units.

2010 census

As of the 2010 census, there were 1,373 people, 610 households, and 397 families in the county. The population density was 1.4 PD/sqmi. There were 845 housing units at an average density of 0.84 /mi2. The racial makeup of the county was 96.6% white, 1.2% American Indian, 0.1% black or African American, 0.0% from other races, and 2.2% from two or more races. Those of Hispanic or Latino origin made up 0.9% of the population. In terms of ancestry, Of the 610 households, 27.0% had children under the age of 18 living with them, 57.5% were married couples living together, 4.6% had a female householder with no husband present, 34.9% were non-families, and 31.6% of all households were made up of individuals. The average household size was 2.25 and the average family size was 2.82. The median age was 46.6 years. The median income for a household in the county was $48,958 and the median income for a family was $58,875. Males had a median income of $34,375 versus $29,087 for females. The per capita income for the county was $26,596. About 4.4% of families and 8.0% of the population were below the poverty line, including 12.8% of those under age 18 and 8.4% of those age 65 or over.

Communities

City

Town

Census-designated place

Unorganized territories

The county organization does not include division into townships. Its area is divided into two areas of unorganized territory: West Sully and East Sully.

Politics

Throughout its history, Sully County has been powerfully Republican. The solitary Democrat to carry Sully County at a Presidential level has been Franklin D. Roosevelt in 1932 during an election heavily influenced by the "Dust Bowl" and Great Depression. Nonetheless, in the following 1936 election, Alf Landon won the county by over twenty percent. Since that time, the Democratic Party has bettered FDR's 1936 effort five times, but only Lyndon Johnson in 1964 has held the GOP to a single-digit margin. In modern times, like almost all of rural America, Sully County has become more and more Republican. The last Democrat to carry one-third of the county's vote was Michael Dukakis in 1988 during an election severely affected by a major drought.

Notable person