Douglas County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 2,835. Its county seat is Armour. The county was established in 1873 and organized in 1882. It is named for Stephen Douglas, Illinois political figure.

The terrain of Douglas County consists of rolling hills, mostly dedicated to agriculture. The county's highest point is on its southwestern boundary, toward the SW corner, at 1,677 ft (511 m) ASL. The terrain slopes to the east. The county has a total area of 434 square miles (1,120 km), of which 432 square miles (1,120 km) is land and 1.9 square miles (4.9 km) (0.4%) is water. It is the second-smallest county in South Dakota by area.

• Corsica Lake

Historical population

Census	Pop.	Note	%±
1890	4,600		—
1900	5,012		9.0%
1910	6,400		27.7%
1920	6,993		9.3%
1930	7,236		3.5%
1940	6,348		−12.3%
1950	5,636		−11.2%
1960	5,113		−9.3%
1970	4,569		−10.6%
1980	4,181		−8.5%
1990	3,746		−10.4%
2000	3,458		−7.7%
2010	3,002		−13.2%
2020	2,835		−5.6%
2023 (est.)	2,838		0.1%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2020

As of the 2020 census, there were 2,835 people, 1,134 households, and 779 families residing in the county. The population density was 6.6 inhabitants per square mile (2.5/km). There were 1,341 housing units.

As of the 2010 census, there were 3,002 people, 1,210 households, and 819 families in the county. The population density was 7.0 inhabitants per square mile (2.7/km). There were 1,439 housing units at an average density of 3.3 units per square mile (1.3 units/km). The racial makeup of the county was 96.6% white, 1.8% American Indian, 0.4% black or African American, 0.1% Asian, 0.3% from other races, and 0.9% from two or more races. Those of Hispanic or Latino origin made up 0.8% of the population. In terms of ancestry, 34.8% were Dutch, 33.9% were German, 5.6% were Norwegian, 5.5% were Irish, 5.4% were Russian, and 5.1% were American.

Of the 1,210 households, 25.5% had children under the age of 18 living with them, 60.8% were married couples living together, 4.2% had a female householder with no husband present, 32.3% were non-families, and 29.1% of all households were made up of individuals. The average household size was 2.33 and the average family size was 2.89. The median age was 48.3 years.

The median income for a household in the county was $42,794 and the median income for a family was $53,750. Males had a median income of $36,689 versus $24,883 for females. The per capita income for the county was $22,200. About 7.2% of families and 9.8% of the population were below the poverty line, including 10.9% of those under age 18 and 15.2% of those age 65 or over.

• Armour (county seat)
• Corsica
• Delmont

• Greenwood Colony
• Harrison
• New Holland

• Joubert

• Douglas City
• Flensburg
• Grand View
• Huston
• Maitland

Douglas County voters have long been reliably Republican. In only two national elections since 1892 has the county selected the Democratic Party candidate.

United States presidential election results for Douglas County, South Dakota

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	1,419	85.59%	219	13.21%	20	1.21%
2020	1,468	86.00%	216	12.65%	23	1.35%
2016	1,338	83.36%	214	13.33%	53	3.30%
2012	1,334	78.93%	332	19.64%	24	1.42%
2008	1,293	73.63%	424	24.15%	39	2.22%
2004	1,596	79.32%	393	19.53%	23	1.14%
2000	1,311	76.71%	363	21.24%	35	2.05%
1996	1,210	63.38%	524	27.45%	175	9.17%
1992	1,175	56.85%	481	23.27%	411	19.88%
1988	1,438	67.23%	695	32.49%	6	0.28%
1984	1,713	76.00%	536	23.78%	5	0.22%
1980	1,855	75.31%	508	20.63%	100	4.06%
1976	1,315	57.30%	975	42.48%	5	0.22%
1972	1,434	61.68%	887	38.15%	4	0.17%
1968	1,613	70.68%	592	25.94%	77	3.37%
1964	1,189	50.86%	1,149	49.14%	0	0.00%
1960	2,002	78.73%	541	21.27%	0	0.00%
1956	1,713	67.81%	813	32.19%	0	0.00%
1952	2,103	79.93%	528	20.07%	0	0.00%
1948	1,301	63.71%	736	36.04%	5	0.24%
1944	1,483	67.35%	719	32.65%	0	0.00%
1940	1,977	65.53%	1,040	34.47%	0	0.00%
1936	1,418	44.75%	1,680	53.01%	71	2.24%
1932	1,045	34.08%	2,005	65.39%	16	0.52%
1928	1,949	68.68%	879	30.97%	10	0.35%
1924	1,125	50.25%	317	14.16%	797	35.60%
1920	1,247	63.49%	386	19.65%	331	16.85%
1916	815	57.48%	597	42.10%	6	0.42%
1912	0	0.00%	714	47.41%	792	52.59%
1908	836	55.99%	647	43.34%	10	0.67%
1904	859	61.89%	499	35.95%	30	2.16%
1900	649	52.85%	567	46.17%	12	0.98%
1896	533	58.06%	380	41.39%	5	0.54%
1892	541	50.85%	109	10.24%	414	38.91%

• National Register of Historic Places listings in Douglas County, South Dakota

43°23′N 98°22′W / 43.39°N 98.36°W / 43.39; -98.36