Lawrence County is the only county in the Spearfish, South Dakota Micropolitan Statistical Area.
As of the census of 2000, there were 21,802 people, 8,881 households, and 5,559 families residing in the county. The population density was 27 people per square mile (11/km²). There were 10,427 housing units at an average density of 13 per square mile (5/km²). The racial makeup of the county was 95.79% White, 0.23% Black or African American, 2.18% Native American, 0.33% Asian, 0.05% Pacific Islander, 0.33% from other races, and 1.08% from two or more races. 1.82% of the population were Hispanic or Latino of any race. 36.0% were of German, 12.0% Norwegian, 9.0% English and 7.5% Irish ancestry according to Census 2000.
There were 8,881 households out of which 28.80% had children under the age of 18 living with them, 51.00% were married couples living together, 8.50% had a female householder with no husband present, and 37.40% were non-families. 29.60% of all households were made up of individuals and 11.50% had someone living alone who was 65 years of age or older. The average household size was 2.33 and the average family size was 2.89.
In the county, the population was spread out with 23.10% under the age of 18, 13.70% from 18 to 24, 25.40% from 25 to 44, 23.10% from 45 to 64, and 14.60% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 96.80 males. For every 100 females age 18 and over, there were 93.30 males.
The median income for a household in the county was $31,755, and the median income for a family was $40,501. Males had a median income of $30,098 versus $19,679 for females. The per capita income for the county was $17,195. About 9.50% of families and 14.80% of the population were below the poverty line, including 15.70% of those under age 18 and 9.10% of those age 65 or over.