Vernon County is a county located in the center of the western border of Missouri. As of the 2010 census, the population was 21,159. Its county seat is Nevada. The county was organized on February 27, 1855, considerably later than counties in the eastern part of the state. It was named for Colonel Miles Vernon (1786–1867), a state senator and veteran of the Battle of New Orleans. This was part of the large historic territory of the Osage Nation of Native Americans.
According to the U.S. Census Bureau, the county has a total area of 837 square miles (2,170 km), of which 826 square miles (2,140 km) is land and 10 square miles (26 km) (1.2%) is water.
As of the census of 2000, there were 20,454 people, 7,966 households, and 5,432 families residing in the county. The population density was 24 people per square mile (9/km²). There were 8,872 housing units at an average density of 11 per square mile (4/km²). The racial makeup of the county was 96.99% White, 0.61% Black or African American, 0.79% Native American, 0.31% Asian, 0.03% Pacific Islander, 0.31% from other races, and 0.95% from two or more races. Approximately 0.84% of the population were Hispanic or Latino of any race.
There were 7,966 households out of which 32.20% had children under the age of 18 living with them, 55.30% were married couples living together, 9.60% had a female householder with no husband present, and 31.80% were non-families. 28.10% of all households were made up of individuals and 13.00% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.97.
In the county, the population was spread out with 26.60% under the age of 18, 9.20% from 18 to 24, 25.40% from 25 to 44, 22.50% from 45 to 64, and 16.30% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 93.50 males. For every 100 females age 18 and over, there were 88.00 males.
The median income for a household in the county was $30,021, and the median income for a family was $37,714. Males had a median income of $28,182 versus $19,026 for females. The per capita income for the county was $15,047. About 10.10% of families and 14.90% of the population were below the poverty line, including 20.30% of those under age 18 and 13.30% of those age 65 or over.