The Atchison Micropolitan Statistical Area includes all of Atchison County.
Atchison County's population was estimated to be 16745 in the year 2006, a decrease of 16, or -0.1%, over the previous six years.
As of the U.S. Census in 2000, there were 16,774 people, 6,275 households, and 4,279 families residing in the county. The population density was 39 people per square mile (15/km²). There were 6,818 housing units at an average density of 16 per square mile (6/km²). The racial makeup of the county was 91.62% White, 5.32% Black or African American, 0.55% Native American, 0.34% Asian, 0.06% Pacific Islander, 0.51% from other races, and 1.59% from two or more races. Hispanic or Latino of any race were 1.95% of the population.
There were 6,275 households out of which 32.40% had children under the age of 18 living with them, 54.30% were married couples living together, 10.00% had a female householder with no husband present, and 31.80% were non-families. 27.60% of all households were made up of individuals and 12.80% had someone living alone who was 65 years of age or older. The average household size was 2.51 and the average family size was 3.05.
In the county the population was spread out with 26.70% under the age of 18, 11.30% from 18 to 24, 24.50% from 25 to 44, 21.40% from 45 to 64, and 16.20% who were 65 years of age or older. The median age was 36 years. For every 100 females there were 93.30 males. For every 100 females age 18 and over, there were 90.30 males.
The median income for a household in the county was $34,355, and the median income for a family was $40,614. Males had a median income of $29,481 versus $20,485 for females. The per capita income for the county was $15,207. About 7.90% of families and 13.30% of the population were below the poverty line, including 13.80% of those under age 18 and 17.90% of those age 65 or over.