Shelby County is a county located in the northeastern portion of the U.S. state of Missouri. As of the 2010 census, the population was 6,373. Its county seat is Shelbyville. The county was organized January 2, 1835 and named for Governor Isaac Shelby of Kentucky.
According to the U.S. Census Bureau, the county has a total area of 502 square miles (1,300 km), of which 501 square miles (1,300 km) is land and 1.5 square miles (3.9 km) (0.3%) is water.
As of the census of 2000, there were 6,799 people, 2,745 households, and 1,847 families residing in the county. The population density was 14 people per square mile (5/km²). There were 3,245 housing units at an average density of 6 per square mile (2/km²). The racial makeup of the county was 97.87% White, 0.97% Black or African American, 0.28% Native American, 0.10% Asian, 0.19% from other races, and 0.59% from two or more races. Approximately 0.63% of the population were Hispanic or Latino of any race. 30.4% were of American, 26.9% German, 14.9% English and 8.5% Irish ancestry.
There were 2,745 households out of which 30.60% had children under the age of 18 living with them, 56.90% were married couples living together, 7.30% had a female householder with no husband present, and 32.70% were non-families. 30.30% of all households were made up of individuals and 16.60% had someone living alone who was 65 years of age or older. The average household size was 2.38 and the average family size was 2.98.
In the county, the population was spread out with 25.40% under the age of 18, 7.20% from 18 to 24, 24.40% from 25 to 44, 23.30% from 45 to 64, and 19.70% who were 65 years of age or older. The median age was 40 years. For every 100 females there were 91.60 males. For every 100 females age 18 and over, there were 90.00 males.
The median income for a household in the county was $29,448, and the median income for a family was $35,944. Males had a median income of $25,759 versus $18,996 for females. The per capita income for the county was $15,632. About 13.00% of families and 16.30% of the population were below the poverty line, including 21.70% of those under age 18 and 14.10% of those age 65 or over.