Organized March 3, 1849, from Newton County and named for Alexander McDonald, Revolutionary War soldier. Originally defined by the Legislature as Seneca County and attached to Newton County for civil and military purposes on January 1, 1847, the name was changed to McDonald upon formal organization of the county.

Persons interested in the early history of our county will enjoy the free online (PDF) book The Sturges History of McDonald County, Missouri

As of the census of 2010, there were 23,083 people (total male population was 11,661 and total female population was 11,422),8404 households, and 6074 families residing in the county. The population density was 16/km2 (40/sq mi). There were 9925 housing units at an average density of 7/km (17 sq mi). The racial makeup of the county was 85% White, .6% Black or African American, 2.9% Native American, 0.8% Asian, 1.1% Pacific Islander, 6.4% from other races, and 3.2% from two or more races. 11.2% of the population was Hispanic or Latino of any race. 11.8% were of American, 12.8% German, 10.8% Irish and 10.2% English ancestry according to Census 2010.

There were 8404 households out of which 37.1% had children under the age of 18 living with them, 55% were married couples living together, 12.4% had a female householder with no husband present, and 3.9% had a male householder with no wife present. 28.7% were non-families. 25.8% of all households were made up of individuals and 9.5% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.36.

In the county the population was spread out with a 30.7% under the age of 18, 5.7% from 18 to 24, 25% from 25 to 44, 26.1 from 45 to 64, and 13.2% who were 65 years of age or older. The median age was 36.5 years.

The median income for a household in the county was $37,701, and the median income for a family was $46,005. Males had a median income of $35,233 versus $30,071 for females. The per capita income for the county was $17,841. About 12.2% of families and 17.5% of the population were below the poverty line, including 22.5% of those under age 18 and 13.9% of those ages 65 or over.

Unincorporated: Rocky Comfort, Longview, Powell, Tiff City, Caverna

McDonald County is part of the Fayetteville-Springdale-Rogers, Ar-Mo Metropolitan Statistical Area.