Wahpeton's twin city is Breckenridge, Minnesota. The Bois de Sioux River and the Otter Tail River join at Wahpeton and Breckenridge to form the Red River of the North.
The North Dakota State College of Science is located in Wahpeton. The local newspaper is the Wahpeton Daily News.
As of the census of 2000, there were 8,586 people, 3,254 households, and 1,867 families residing in the city. The population density was 663.0/km² (1,718.1/mi²). There were 3,492 housing units at an average density of 269.7/km² (698.8/mi²). The racial makeup of the city was 95.47% White, 0.62% African American, 2.41% Native American, 0.43% Asian, 0.03% Pacific Islander, 0.12% from other races, and 0.92% from two or more races. Hispanic or Latino of any race were 0.76% of the population.
The top 6 ancestry groups in the city are German (47.4%), Norwegian (28.4%), Irish (7.1%), Swedish (5.8%), French (4.0%), English (4.0%).
There were 3,254 households out of which 30.4% had children under the age of 18 living with them, 45.3% were married couples living together, 8.5% had a female householder with no husband present, and 42.6% were non-families. 32.7% of all households were made up of individuals and 10.0% had someone living alone who was 65 years of age or older. The average household size was 2.28 and the average family size was 2.97.
In the city the population was spread out with 21.2% under the age of 18, 24.1% from 18 to 24, 24.2% from 25 to 44, 17.5% from 45 to 64, and 13.0% who were 65 years of age or older. The median age was 29 years. For every 100 females there were 109.8 males. For every 100 females age 18 and over, there were 112.3 males.
The median income for a household in the city was $33,471, and the median income for a family was $44,645. Males had a median income of $30,199 versus $20,089 for females. The per capita income for the city was $15,293. About 7.3% of families and 13.4% of the population were below the poverty line, including 8.9% of those under age 18 and 10.4% of those age 65 or over.