McDonald County is part of the Fayetteville–Springdale–Rogers, AR-MO Metropolitan Statistical Area.
As of the census of 2000, there were 21,681 people, 8,113 households, and 5,865 families residing in the county. The population density was 40 people per square mile (16/km²). There were 9,287 housing units at an average density of 17 per square mile (7/km²). The racial makeup of the county was 89.66% White, 0.18% Black or African American, 2.88% Native American, 0.14% Asian, 0.14% Pacific Islander, 3.70% from other races, and 3.30% from two or more races. 9.36% of the population were Hispanic or Latino of any race. 28.0% were of American, 11.5% German, 10.5% Irish and 6.6% English ancestry according to Census 2000.
There were 8,113 households out of which 35.70% had children under the age of 18 living with them, 57.60% were married couples living together, 9.60% had a female householder with no husband present, and 27.70% were non-families. 23.30% of all households were made up of individuals and 9.10% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.11.
In the county the population was spread out with 28.90% under the age of 18, 8.70% from 18 to 24, 28.60% from 25 to 44, 22.60% from 45 to 64, and 11.30% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 102.60 males. For every 100 females age 18 and over, there were 99.50 males.
The median income for a household in the county was $27,010, and the median income for a family was $31,530. Males had a median income of $23,434 versus $18,157 for females. The per capita income for the county was $13,175. About 15.60% of families and 20.70% of the population were below the poverty line, including 28.60% of those under age 18 and 17.20% of those age 65 or over.