It was formed out of Green County in 1801.
Adair County also has one of the few remaining American Chestnut trees in America.
Adair County is a prohibition or completely dry county. It is represented in District 51 in the Kentucky House of Representatives by the Republican, John "Bam" Carney of Campbellsville, the seat of Taylor County.
As of the census of 2000, there were 17,244 people, 6,747 households, and 4,803 families residing in the county. The population density was 42 per square mile (16 /km). There were 7,792 housing units at an average density of 19 per square mile (7.3 /km). The racial makeup of the county was 96.00% White, 2.55% Black or African American, 0.22% Native American, 0.26% Asian, 0.02% Pacific Islander, 0.19% from other races, and 0.76% from two or more races. 0.77% of the population were Hispanic or Latino of any race.
There were 6,747 households out of which 31.50% had children under the age of 18 living with them, 57.60% were married couples living together, 10.20% had a female householder with no husband present, and 28.80% were non-families. 26.20% of all households were made up of individuals and 13.00% had someone living alone who was 65 years of age or older. The average household size was 2.44 and the average family size was 2.93.
In the county the population was spread out with 23.50% under the age of 18, 10.70% from 18 to 24, 27.70% from 25 to 44, 23.40% from 45 to 64, and 14.60% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 94.00 males. For every 100 females age 18 and over, there were 91.60 males.
The median income for a household in the county was $24,055, and the median income for a family was $29,779. Males had a median income of $23,183 versus $17,009 for females. The per capita income for the county was $14,931. About 18.20% of families and 24.00% of the population were below the poverty line, including 29.60% of those under age 18 and 21.70% of those age 65 or over.