Osage County's population was estimated to be 16,958 in the year 2006, an increase of 191, or +1.1%, over the previous six years.
As of the U.S. Census in 2000, 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/km²). There were 7,018 housing units at an average density of 10 per square mile (4/km²). 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.