Nemaha County (standard abbreviation: NM) is a county located in the northeastern part of the U.S. state of Kansas. As of the 2010 census, the county population was 10,178 with a 2018 estimate of 10,155. The county seat is Seneca.
According to the U.S. Census Bureau, the county has a total area of 719 square miles (1,860 km), of which 717 square miles (1,860 km) is land and 2.0 square miles (5.2 km) (0.3%) is water.
As of the census of 2000, there were 10,717 people, 3,959 households, and 2,763 families residing in the county. The population density was 15 people per square mile (6/km²). There were 4,340 housing units at an average density of 6 per square mile (2/km²). The racial makeup of the county was 98.35% White, 0.49% Black or African American, 0.23% Native American, 0.10% Asian, 0.06% Pacific Islander, 0.17% from other races, and 0.60% from two or more races. 0.71% of the population were Hispanic or Latino of any race.
There were 3,959 households out of which 34.00% had children under the age of 18 living with them, 61.90% were married couples living together, 5.10% had a female householder with no husband present, and 30.20% were non-families. 28.00% of all households were made up of individuals and 16.00% had someone living alone who was 65 years of age or older. The average household size was 2.58 and the average family size was 3.20.
In the county, the population was spread out with 28.50% under the age of 18, 6.00% from 18 to 24, 24.10% from 25 to 44, 19.40% from 45 to 64, and 22.00% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 97.00 males. For every 100 females age 18 and over, there were 95.10 males.
The median income for a household in the county was $34,296, and the median income for a family was $41,838. Males had a median income of $28,879 versus $19,340 for females. The per capita income for the county was $17,121. About 6.50% of families and 9.10% of the population were below the poverty line, including 9.90% of those under age 18 and 8.50% of those age 65 or over.