Otter Tail County is a county in the U.S. state of Minnesota. As of the 2010 United States Census, the population was 57,303. Its county seat is Fergus Falls.
The Otter Tail River flows south and west through the central and western parts of the county on its way to form the Red River in Wilkin County. It is joined by the south-flowing Pelican River west of Fergus Falls. The Leaf River rises in the county and flows east to its confluence with the Crow Wing River in neighboring Wadena County. The Redeye River flows southeast through the county’s northeast section toward its confluence with the Leaf in Wadena. The county terrain consists of rolling hills, heavily wooded through its center section, dotted with lakes and ponds, and carved with drainages and gullies. The available area is devoted to agriculture. The county terrain slopes to the west and south. The highest point on the county terrain is attributed to two different points: Inspiration Peak, at 1,750′ (533m); or an unnamed rise located 1.3 miles (2.1 km) WNW of Perch Lake, at 1,790′ (546m) ASL. Satellite data supports the probability that the point WNW of Perch Lake is higher. The county has a total area of 2,225 square miles (5,760 km), of which 1,972 square miles (5,110 km) are land and 252 square miles (650 km) (11%) are covered by water. Otter Tail is one of 17 Minnesota savanna region counties with more savanna soils than either forest or prairie soils. According to its website, the county contains over 1,000 lakes.
As of the 2000 United States Census, there were 57,159 people, 22,671 households, and 15,779 families in the county. The population density was 29.0/sqmi (11.2/km²). There were 33,862 housing units at an average density of 17.2/sqmi (6.63/km²). The racial makeup of the county was 97.11% White, 0.29% African American, 0.51% Native American, 0.44% Asian, 0.05% Pacific Islander, 0.84% from other races, and 0.78% from two or more races. Hispanic or Latino of any race were 1.67% of the population. 35.5% were of German and 31.2% Norwegian ancestry.
There were 22,671 households out of which 30.3% had children under the age of 18 living with them, 60.1% were married couples living together, 6.1% had a female householder with no husband present, and 30.4% were non-families. 26.6% of all households were made up of individuals and 13.30% had someone living alone who was 65 years of age or older. The average household size was 2.46 and the average family size was 2.98.
The county population contained 24.9% under the age of 18, 7.2% from 18 to 24, 24.2% from 25 to 44, 24.7% from 45 to 64, and 19.0% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 100.4 males. For every 100 females age 18 and over, there were 97.8 males.
The median income for a household in the county was $35,395, and the median income for a family was $42,740. Males had a median income of $30,151 versus $20,930 for females. The per capita income for the county was $18,014. About 6.7% of families and 10.1% of the population were below the poverty line, including 12.1% of those under age 18 and 11.1% of those age 65 or over.