As of the census of 2000, there were 55,532 people, 23,185 households, and 14,444 families residing in the city of Bismarck. The population density was 797.4/km² (2,065.2/mi²). There were 24,217 housing units at an average density of 347.7/km² (900.6/mi²). The racial makeup of the city was 94.78% White, 0.28% Black or African American, 3.39% Native American, 0.45% Asian, 0.03% Pacific Islander, 0.17% from other races, and 0.89% from two or more races. 0.75% of the population were Hispanic or Latino of any race.

The top six ancestries in the city are: German (57.9%), Norwegian (18.2%), Russian (7.7%), Irish (7.2%), English (5.0%), Swedish (4.3%).

There were 23,185 households out of which 30.2% had children under the age of 18 living with them, 50.1% were married couples living together, 9.3% had a female householder with no husband present, and 37.7% were non-families. 31.0% of all households were made up of individuals and 10.5% had someone living alone who was 65 years of age or older. The average household size was 2.32 and the average family size was 2.94.

In the city, the population was spread out with 23.5% under the age of 18, 11.1% from 18 to 24, 29.1% from 25 to 44, 22.4% from 45 to 64, and 13.8% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 93.9 males. For every 100 females age 18 and over, there were 91.8 males.

The median income per household in the city was $39,422, and the median income per family was $51,477. Males had a median income of $33,804 versus $22,647 for females. The per capita income for the city was $20,789. About 5.7% of families and 8.4% of the population were below the poverty line, including 9.5% of those under age 18 and 7.4% of those age 65 or over.

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