Washington County is a county in the U.S. state of Minnesota. As of the 2020 census, the population was 267,568, making it the fifth-most populous county in Minnesota. Its county seat is Stillwater. The largest city in the county is Woodbury, the eighth-largest city in Minnesota and the fourth-largest Twin Cities suburb. Washington County is included in the Minneapolis-St. Paul-Bloomington, MN-WI Metropolitan Statistical Area.

Early development in the area was on the St. Croix River, which now forms the boundary with Wisconsin on the county's eastern side. The river provided a waterway to move settlers upstream and to transport logs downstream. The heavily forested area fostered an early logging and lumber economy. The area's first settlers arrived at the future Afton in 1837. In 1838 settlers started Dacotah, at the north edge of present Stillwater, at the junction of Brown's Creek and the St. Croix. The creek's name is from the founder of this settlement, Joseph Renshaw Brown. However, a sawmill was built at Marine-on-St.-Croix in 1839, and another was built in the current location of downtown Stillwater in 1844. The success of these soon attracted the settlers from Dacotah, and that community declined.

This area was part of Wisconsin Territory until the eastern part of that territory achieved statehood in 1848. Brown and other leaders called a meeting (the "Stillwater Convention") on August 26, 1848. The convention drafted a Memorial to Congress that a new territory be created with the name “Minnesota,” and elected Henry Hastings Sibley to deliver this citizens' petition to the U.S. Congress. Because of this convention, Stillwater calls itself the “Birthplace of Minnesota.” Congress responded by creating Minnesota Territory effective March 3, 1849.

The newly established territorial legislature created nine counties across the territory in October 1849. Washington County was one of the nine, named for George Washington, with Stillwater named as county seat. The county's first sheriff was appointed in 1849, and the county's school district began in 1850.

After the forests were depleted, the economy of Washington County became primarily agricultural. With the growth of neighboring Ramsey County and St. Paul, some of Washington County developed based on tourism and recreation, as with Mahtomedi and Landfall. Late in the 20th century, the population greatly increased with the suburban expansion of St. Paul.

Washington County lies on the east side of Minnesota. Its east border abuts the west border of the state of Wisconsin (across the St. Croix River). The Mississippi River flows south-southeastward west of Washington County, and forms the southwest border of the county as it flows toward its confluence with the St. Croix (at the county's southernmost point). Washington County terrain consists of low rolling hills, sloping to the south and east, with its highest point on the lower west border at 1,053 ft (321 m) ASL. The county has a total area of 423 square miles (1,100 km), of which 384 square miles (990 km) is land and 38 square miles (98 km) (9.1%) is water. It is the fourth-smallest county in Minnesota by land area and fifth-smallest by total area.

• Forest Lake Airport (25D) - south of Forest Lake
• Lake Elmo Airport (21D) - northeast of Lake Elmo

Historical population

Census	Pop.	Note	%±
1850	1,056		—
1860	6,123		479.8%
1870	11,809		92.9%
1880	19,563		65.7%
1890	25,992		32.9%
1900	27,808		7.0%
1910	26,013		−6.5%
1920	23,761		−8.7%
1930	24,753		4.2%
1940	26,430		6.8%
1950	34,544		30.7%
1960	52,432		51.8%
1970	83,003		58.3%
1980	113,571		36.8%
1990	145,896		28.5%
2000	201,130		37.9%
2010	238,136		18.4%
2020	267,568		12.4%
2023 (est.)	278,936		4.2%
U.S. Decennial Census 1790-1960 1900-1990 1990-2000 2010-2020

Washington County, Minnesota - Demographic Profile
(NH = Non-Hispanic)

Race / Ethnicity	Pop 2010	Pop 2020	% 2010	% 2020
White alone (NH)	204,111	208,277	85.71%	77.84%
Black or African American alone (NH)	8,376	13,799	3.52%	5.16%
Native American or Alaska Native alone (NH)	973	999	0.41%	0.37%
Asian alone (NH)	12,023	18,530	5.05%	6.93%
Pacific Islander alone (NH)	72	72	0.03%	0.03%
Some Other Race alone (NH)	214	969	0.09%	0.36%
Mixed Race/Multi-Racial (NH)	4,240	11,828	1.78%	4.42%
Hispanic or Latino (any race)	8,127	13,094	3.41%	4.89%
Total	238,136	267,568	100.00%	100.00%

Note: the US Census treats Hispanic/Latino as an ethnic category. This table excludes Latinos from the racial categories and assigns them to a separate category. Hispanics/Latinos can be of any race.

The ethnic makeup of the country, according to the 2010 census, was the following:

• 87.77% White
• 3.60% Black
• 0.49% Native American
• 5.07% Asian
• >0.01% Native Hawaiian or Pacific Islander
• 2.10% Two or more races
• 0.97% Other races
• 3.41% Hispanic or Latino (of any race)

As of the census of 2010, there were 238,136 people, 87,446 households, and 64,299 families in the county. The population density was 620 per square mile (240/km). There were 87,446 housing units at an average density of 228 per square mile (88/km). 39.4% were of German, 14.4% Irish, 13.0% Norwegian, and 9.9% Swedish ancestry. There were 87,446 households, out of which 38.6% had children under the age of 18 living with them, 60.6% were married couples living together, 9.5% had a female householder with no husband present, and 26.5% were non-families. 21.5% of all households were made up of individuals, and 7.3% had someone living alone who was 65 years of age or older. The average household size was 2.67 and the average family size was 3.14.

The county population contained 23.5% under the age of 18, 6.2% from 18 to 24, 32.90% from 25 to 44, 28.7% from 45 to 64, and 10.3% who were 65 years of age or older. The median age was 38 years. For every 100 females there were 98.02 males. For every 100 females age 18 and over, there were 97.03 males. The median income for a household in the county was $79,735, and the median income for a family was $92,497. The per capita income for the county was $36,786. About 5.2% of the population was below the poverty line.

According to the 2007-2011 American Community Survey, of the county's population 25 years and over, 1.4% had less than 9th grade education, 2.8% held 9th to 12th grade with no diploma, 23.6% had High school graduate or equivalent, 22.2% held Some college with no degree, 27.0% had bachelor's degree, and 13.0% earned Graduate or professional degree.

As of the census of 2000, there were 201,130 people, 71,462 households, and 54,668 families in the county. The population density was 524 per square mile (202/km). There were 73,635 housing units at an average density of 192 per square mile (74/km). The racial makeup of the county was 93.63% White, 1.83% Black or African American, 0.39% Native American, 2.14% Asian, 0.03% Pacific Islander, 0.60% from other races, and 1.37% from two or more races.

There were 71,462 households, out of which 41.60% had children under the age of 18 living with them, 64.80% were married couples living together, 8.50% had a female householder with no husband present, and 23.50% were non-families. 18.70% of all households were made up of individuals, and 5.40% had someone living alone who was 65 years of age or older. The average household size was 2.77 and the average family size was 3.19.

The county population contained 29.40% under the age of 18, 6.80% from 18 to 24, 32.90% from 25 to 44, 23.20% from 45 to 64, and 7.60% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 98.80 males. For every 100 females age 18 and over, there were 96.80 males.

The median income for a household in the county was $66,305, and the median income for a family was $74,576 (these figures had risen to $78,067 and $90,867 respectively as of a 2007 estimate). Males had a median income of $49,815 versus $33,804 for females. The per capita income for the county was $28,148. About 2.00% of families and 2.90% of the population were below the poverty line, including 3.50% of those under age 18 and 4.10% of those age 65 or over.

Washington County voters slightly tend to vote Democratic. In 70% of national elections since 1948, the county selected the Democratic Party candidate (as of 2024). It voted for the national winner in every election from 1992 to 2012.

United States presidential election results for Washington County, Minnesota

Year	Republican		Democratic		Third party(ies)
	No.	%	No.	%	No.	%
2024	75,271	44.40%	90,324	53.28%	3,941	2.32%
2020	73,764	44.23%	89,165	53.46%	3,857	2.31%
2016	64,428	44.67%	67,086	46.51%	12,721	8.82%
2012	69,137	48.64%	70,203	49.39%	2,793	1.97%
2008	64,334	46.94%	70,277	51.27%	2,448	1.79%
2004	65,751	51.19%	61,395	47.80%	1,303	1.01%
2000	51,502	48.13%	49,637	46.39%	5,870	5.49%
1996	31,219	35.45%	45,119	51.24%	11,719	13.31%
1992	26,568	31.07%	35,820	41.90%	23,111	27.03%
1988	30,850	46.45%	34,952	52.63%	613	0.92%
1984	29,046	50.13%	28,527	49.23%	369	0.64%
1980	22,718	41.38%	25,634	46.69%	6,550	11.93%
1976	20,716	42.64%	26,454	54.45%	1,413	2.91%
1972	19,142	53.03%	16,102	44.61%	854	2.37%
1968	10,921	37.72%	16,449	56.81%	1,584	5.47%
1964	8,850	32.75%	18,108	67.01%	64	0.24%
1960	11,202	48.42%	11,870	51.31%	61	0.26%
1956	9,562	56.06%	7,462	43.75%	32	0.19%
1952	9,408	54.57%	7,768	45.06%	64	0.37%
1948	5,686	40.70%	8,039	57.54%	245	1.75%
1944	6,014	51.49%	5,599	47.94%	66	0.57%
1940	6,710	51.41%	6,288	48.18%	54	0.41%
1936	3,863	32.99%	6,768	57.80%	1,079	9.21%
1932	3,996	37.50%	6,413	60.18%	247	2.32%
1928	6,113	59.06%	4,158	40.17%	80	0.77%
1924	4,482	52.40%	699	8.17%	3,372	39.42%
1920	5,852	74.84%	1,558	19.93%	409	5.23%
1916	2,167	53.55%	1,610	39.78%	270	6.67%
1912	581	13.76%	1,289	30.52%	2,353	55.72%
1908	2,727	68.50%	1,120	28.13%	134	3.37%
1904	2,913	79.94%	652	17.89%	79	2.17%
1900	2,984	68.49%	1,279	29.36%	94	2.16%
1896	3,995	70.51%	1,558	27.50%	113	1.99%
1892	2,451	53.31%	1,733	37.69%	414	9.00%

Like all counties in Minnesota, Washington is governed by an elected and nonpartisan board of commissioners. Each commissioner represents a district of approximately equal population.

Washington County is divided among three congressional districts. Northern Washington County is represented by Minnesota's 6th congressional district (CPVI R+12), central Washington County by Minnesota's 4th congressional district (CPVI D+14), and southern Washington County by Minnesota's 2nd congressional district (CPVI EVEN).

According to the county's 2021 Annual Comprehensive Financial Report, the top employers in the county are:

#	Employer	# of Employees
1	Andersen Corporation (Bayport)	4,939
2	Independent School District 833	2,594
3	Woodwinds Healtheast Campus	1,331
4	Washington County Government	1,324
5	Walmart	1,274
6	Hy-Vee Grocery	1,250
7	Independent School District 834	1,136
8	Independent School District 831	1,074
9	Target Corporation	959
10	Bailey Nurseries, Inc	800

• Afton State Park
• Afton Alps Ski Area
• Gateway State Trail
• William O'Brien State Park

• Garen
• Point Douglas

Washington County has had three locations listed as Environmental Protection Agency Superfund sites due to soil and groundwater contamination. The Baytown Township Ground Water Plume and the Oakdale Dump are currently listed, while the Washington County Landfill was cleaned up and removed from the Superfund list in 1996.

• National Register of Historic Places listings in Washington County, Minnesota
• List of Superfund sites in Minnesota

• Washington County official government’s website
• Washington County Parks
• Washington County Sheriff's Office
• Washington County Historical Society

UScensus1990 45°02′N 92°53′W / 45.04°N 92.89°W / 45.04; -92.89