The county was created on May 23, 1857, named for the river in Germantown Township. Minnesota Governor Horace Austin appointed three county commissioners when the county was established. They met at a home about six miles northwest of Windom on the Des Moines River at Big Bend. During this meeting, they designated the commissioners' districts and changed various county officers. The county organization was completed on July 29, 1870. The first general election was held in the county that November. The first deed of record was filed on January 10, 1870. The first land assessments were made in 1871, and the first taxes were paid in 1872.
Mountain Park, southeast of Mountain Lake, has been listed on the National Register of Historic Places since 1973. A 1976 archeological dig unearthed evidence of a Fox Indian habitation there circa 500 B.C., the oldest human habitation to be discovered in Minnesota.
The Heron Lake Outflow flows east through the lower part of Cottonwood County. The county terrain consists of low rolling hills, devoted to agriculture. The terrain generally slopes to the east, with the northern portion also sloping north and the lower portion sloping south. The highest point is on the midpoint of the west border, at 1,535' ASL. The county has an area of, of which is land and is water.
Watersheds
The northeastern part of the county drains north to the Minnesota River through numerous small creeks, the Cottonwood River and Watonwan River. The southwestern part drains south through the Des Moines River. These two watersheds come together at the Mississippi River near Keokuk, Iowa. Most wetlands in the county have been drained for agricultural use.
As of the 2000 United States Census, there were 12,167 people, 4,917 households, and 3,338 families in the county. The population density was 19.0/sqmi. There were 5,376 housing units at an average density of 8.41/sqmi. The racial makeup of the county was 95.23% White, 0.34% Black or African American, 0.23% Native American, 1.63% Asian, 0.08% Pacific Islander, 1.35% from other races, and 1.14% from two or more races. 2.19% of the population were Hispanic or Latino of any race. 50.2% were of German and 18.6% Norwegian ancestry. There were 4,917 households out of which 28.60% had children under the age of 18 living with them, 58.10% were married couples living together, 6.90% had a female householder with no husband present, and 32.10% were non-families. 28.90% of all households were made up of individuals and 15.90% had someone living alone who was 65 years of age or older. The average household size was 2.39 and the average family size was 2.94. The county population contained 25.00% under the age of 18, 6.50% from 18 to 24, 23.20% from 25 to 44, 23.20% from 45 to 64, and 22.10% who were 65 years of age or older. The median age was 42 years. For every 100 females there were 94.50 males. For every 100 females age 18 and over, there were 91.50 males. The median income for a household in the county was $31,943, and the median income for a family was $40,237. Males had a median income of $28,993 versus $19,934 for females. The per capita income for the county was $16,647. About 7.40% of families and 11.70% of the population were below the poverty line, including 18.40% of those under age 18 and 8.70% of those age 65 or over.
Government and politics
Cottonwood County reliably votes Republican. In only one presidential election since 1964 has it selected the Democratic candidate.
