Osage County (county code OS) is a county located in the U.S. state of Kansas. As of the 2010 census, the county population was 16,295. Its county seat is Lyndon, and its most populous city is Osage City. The county was originally organized in 1855 as Weller County, and was renamed in 1859 after the Osage River that runs through it, which is itself named for the Osage Native American Tribe.
According to the U.S. Census Bureau, the county has a total area of 720 square miles (1,900 km), of which 706 square miles (1,830 km) is land and 14 square miles (36 km) (2.0%) is water.
Osage County is included in the Topeka Metropolitan Statistical Area.
As of the 2000 census, there were 16,712 people, 6,490 households, and 4,737 families residing in the county. The population density was 24 people per square mile (9/km). There were 7,018 housing units at an average density of 10 per square mile (4/km). The racial makeup of the county was 97.27% White, 0.22% Black or African American, 0.65% Native American, 0.17% Asian, 0.10% Pacific Islander, 0.41% from other races, and 1.18% from two or more races. Hispanic or Latino of any race were 1.53% of the population.
There were 6,490 households out of which 33.80% had children under the age of 18 living with them, 61.00% were married couples living together, 8.10% had a female householder with no husband present, and 27.00% were non-families. 23.50% of all households were made up of individuals and 11.50% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 2.99.
In the county, the population was spread out with 27.00% under the age of 18, 6.40% from 18 to 24, 27.00% from 25 to 44, 23.70% from 45 to 64, and 15.80% who were 65 years of age or older. The median age was 39 years. For every 100 females, there were 96.00 males. For every 100 females age 18 and over, there were 93.30 males.
The median income for a household in the county was $37,928, and the median income for a family was $44,581. Males had a median income of $30,670 versus $22,981 for females. The per capita income for the county was $17,691. About 6.40% of families and 8.40% of the population were below the poverty line, including 8.40% of those under age 18 and 10.40% of those age 65 or over.