Doniphan County (county code DP) is a county located in the U.S. state of Kansas and is included in the St Joseph metropolitan area and is part of the Kansas City-Overland Park-Kansas City Combined statistical area. As of the 2010 census, the county population was 7,945 with a 2018 estimate of 7,682. Its county seat is Troy, and its most populous city is Wathena.
Doniphan County is located in the northeastern corner of the state—it is bordered by Nebraska to the north and Missouri to the east. According to the U.S. Census Bureau, the county has a total area of 398 square miles (1,030 km), of which 393 square miles (1,020 km) is land and 4.9 square miles (13 km) (1.2%) is water. It is the third-smallest county in Kansas by land area and second-smallest by total area.
Doniphan County is included in the St. Joseph, MO-KS Metropolitan Statistical Area, which is also included in the Kansas City-Overland Park-Kansas City, MO-KS Combined Statistical Area.
As of the 2000 census, there were 8,249 people, 3,173 households, and 2,183 families residing in the county. The population density was 21 people per square mile (8/km²). There were 3,489 housing units at an average density of 9 per square mile (3/km²). The racial makeup of the county was 94.85% White, 2.00% Black or African American, 1.21% Native American, 0.25% Asian, 0.40% from other races, and 1.29% from two or more races. Hispanic or Latino of any race were 1.16% of the population.
There were 3,173 households out of which 32.60% had children under the age of 18 living with them, 56.40% were married couples living together, 8.70% had a female householder with no husband present, and 31.20% were non-families. 27.60% of all households were made up of individuals and 14.20% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.03.
In the county, the population was spread out with 25.30% under the age of 18, 11.80% from 18 to 24, 24.70% from 25 to 44, 22.00% from 45 to 64, and 16.20% who were 65 years of age or older. The median age was 37 years. For every 100 females, there were 98.60 males. For every 100 females age 18 and over, there were 96.20 males.
The median income for a household in the county was $32,537, and the median income for a family was $39,357. Males had a median income of $28,096 versus $19,721 for females. The per capita income for the county was $14,849. About 9.00% of families and 11.90% of the population were below the poverty line, including 13.30% of those under age 18 and 12.50% of those age 65 or over.