As of the census of 2000, there were 8,606 people, 3,638 households, and 1,931 families residing in the city. The population density was 1,409.1 people per square mile (543.8/km²). There were 3,904 housing units at an average density of 639.2/sq mi (246.7/km²). The racial makeup of the city was 95.33% White, 0.35% African American, 2.31% Native American, 0.36% Asian, 0.02% Pacific Islander, 0.33% from other races, and 1.30% from two or more races. Hispanic or Latino of any race were 1.73% of the population. 37.5% were of German, 13.5% Norwegian, 9.6% English and 8.2% Irish ancestry according to Census 2000.
There were 3,638 households out of which 25.2% had children under the age of 18 living with them, 41.4% were married couples living together, 9.2% had a female householder with no husband present, and 46.9% were non-families. 37.0% of all households were made up of individuals and 15.5% had someone living alone who was 65 years of age or older. The average household size was 2.15 and the average family size was 2.85.
In the city the population was spread out with 20.3% under the age of 18, 21.5% from 18 to 24, 23.3% from 25 to 44, 17.9% from 45 to 64, and 17.1% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 87.1 males. For every 100 females age 18 and over, there were 83.3 males.
The median income for a household in the city was $26,887, and the median income for a family was $40,257. Males had a median income of $30,242 versus $20,431 for females. The per capita income for the city was $16,565. About 9.8% of families and 17.4% of the population were below the poverty line, including 16.1% of those under age 18 and 9.4% of those age 65 or over.
Spearfish has two bus and coach transport services; Dakota Trailways and Prairie Hills Transit.