Codington County is a county in the U.S. state of South Dakota. As of the 2020 census, the population was 28,325, making it the 7th most populous county in South Dakota. Its county seat is Watertown. The county was created in 1877 and organized in 1878. It is named for Rev. George S. S. Codington, Dakota Territory legislator.

Codington County comprises the Watertown, SD Micropolitan Statistical Area.

Codington County terrain consists of rolling hills dotted with lakes and ponds, especially in the southwest 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 717 square miles (1,860 km), of which 688 square miles (1,780 km) is land and 29 square miles (75 km) (4.0%) is water.

• Jefferson Lines

Historical population

Census	Pop.	Note	%±
1880	2,156		—
1890	7,037		226.4%
1900	8,770		24.6%
1910	14,092		60.7%
1920	16,549		17.4%
1930	17,457		5.5%
1940	17,014		−2.5%
1950	18,944		11.3%
1960	20,220		6.7%
1970	19,140		−5.3%
1980	20,885		9.1%
1990	22,698		8.7%
2000	25,897		14.1%
2010	27,227		5.1%
2020	28,325		4.0%
2023 (est.)	28,971		2.3%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2020

As of the 2020 census, there were 28,325 people, 12,026 households, and 7,199 families residing in the county. The population density was 41.2 inhabitants per square mile (15.9/km). There were 13,211 housing units.

As of the 2010 census, there were 27,227 people, 11,432 households, and 7,216 families in the county. The population density was 39.5 inhabitants per square mile (15.3/km). There were 12,397 housing units at an average density of 18.0 per square mile (6.9/km). 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.

• Watertown (county seat)

• Waverly

Codington County voters have been reliably Republican for several decades. In no national election since 1976 has the county selected the Democratic Party candidate.

United States presidential election results for Codington County, South Dakota

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2020	8,958	68.06%	3,837	29.15%	366	2.78%
2016	7,764	66.54%	3,174	27.20%	731	6.26%
2012	6,696	58.10%	4,588	39.81%	240	2.08%
2008	6,374	52.31%	5,595	45.92%	216	1.77%
2004	7,778	61.00%	4,803	37.67%	170	1.33%
2000	6,718	60.32%	4,192	37.64%	228	2.05%
1996	4,995	45.18%	4,722	42.71%	1,338	12.10%
1992	3,943	36.03%	3,701	33.82%	3,299	30.15%
1988	5,050	51.99%	4,570	47.05%	94	0.97%
1984	6,108	63.11%	3,528	36.45%	42	0.43%
1980	5,903	59.09%	3,353	33.56%	734	7.35%
1976	4,504	48.89%	4,680	50.80%	29	0.31%
1972	4,936	51.61%	4,601	48.11%	27	0.28%
1968	3,929	46.49%	4,235	50.11%	288	3.41%
1964	3,593	40.16%	5,353	59.84%	0	0.00%
1960	5,309	55.23%	4,304	44.77%	0	0.00%
1956	5,150	57.72%	3,772	42.28%	0	0.00%
1952	5,750	65.91%	2,974	34.09%	0	0.00%
1948	3,349	45.01%	4,042	54.32%	50	0.67%
1944	3,348	51.76%	3,120	48.24%	0	0.00%
1940	4,320	53.83%	3,705	46.17%	0	0.00%
1936	3,005	39.44%	4,256	55.85%	359	4.71%
1932	2,538	34.32%	4,806	64.98%	52	0.70%
1928	3,762	53.08%	3,299	46.55%	26	0.37%
1924	1,862	41.38%	627	13.93%	2,011	44.69%
1920	2,706	59.84%	867	19.17%	949	20.99%
1916	1,550	51.82%	1,344	44.93%	97	3.24%
1912	0	0.00%	1,111	45.03%	1,356	54.97%
1908	1,618	63.30%	831	32.51%	107	4.19%
1904	1,741	72.18%	582	24.13%	89	3.69%
1900	1,225	58.28%	805	38.30%	72	3.43%
1896	1,041	57.10%	759	41.63%	23	1.26%
1892	882	52.16%	408	24.13%	401	23.71%

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

44°59′N 97°11′W / 44.98°N 97.18°W / 44.98; -97.18