Marshall County is a county located on the south central border of Oklahoma. As of the 2010 census, the population was 15,840. Its county seat is Madill. The county was created at statehood in 1907 from the former Pickens County of the Chickasaw Nation. It was named to honor the maiden name of the mother of George Henshaw, a member of the 1906 Oklahoma Constitutional Convention. The county and its cities are part of the Texoma region.
According to the U.S. Census Bureau, the county has a total area of 427 square miles (1,110 km), of which 371 square miles (960 km) is land and 56 square miles (150 km) (13%) is water. It is the smallest county in Oklahoma by land area and the third-smallest by total area. The Red River drains the county and formed the county’s southern boundary. Completion of the Denison Dam in 1942 created Lake Texoma which inundated part of Marshall County’s land area and forms the current southern boundary and the eastern boundary of the county as well.
As of the census of 2000, there were 13,184 people, 5,371 households, and 3,802 families residing in the county. The population density was 36 people per square mile (14/km²). There were 8,517 housing units at an average density of 23 per square mile (9/km²). The racial makeup of the county was 77.99% White, 1.84% Black or African American, 9.10% Native American, 0.19% Asian, 0.01% Pacific Islander, 6.17% from other races, and 4.71% from two or more races. 8.60% of the population were Hispanic or Latino of any race.
There were 5,371 households out of which 27.30% had children under the age of 18 living with them, 58.10% were married couples living together, 8.80% had a female householder with no husband present, and 29.20% were non-families. 26.40% of all households were made up of individuals and 14.50% had someone living alone who was 65 years of age or older. The average household size was 2.40 and the average family size was 2.87.
In the county, the population was spread out with 23.50% under the age of 18, 7.50% from 18 to 24, 24.10% from 25 to 44, 25.50% from 45 to 64, and 19.50% who were 65 years of age or older. The median age was 41 years. For every 100 females there were 96.50 males. For every 100 females age 18 and over, there were 93.60 males.
The median income for a household in the county was $26,437, and the median income for a family was $31,825. Males had a median income of $25,201 versus $19,932 for females. The per capita income for the county was $14,982. About 13.50% of families and 17.90% of the population were below the poverty line, including 24.10% of those under age 18 and 15.30% of those age 65 or over.