According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. The western half of Cook County, roughly west of Interstate 75, is located in the Little River sub-basin of the Suwannee River basin. The eastern half of the county is located in the Withlacoochee River sub-basin of the same Suwannee River basin.
As of the census of 2000, there were 15,771 people, 5,882 households, and 4,282 families living in the county. The population density was 69 people per square mile. There were 6,558 housing units at an average density of 29 per square mile. The racial makeup of the county was 67.93% White, 29.09% Black or African American, 0.22% Native American, 0.42% Asian, 0.03% Pacific Islander, 1.53% from other races, and 0.78% from two or more races. 3.08% of the population were Hispanic or Latino of any race. There were 5,882 households out of which 34.80% had children under the age of 18 living with them, 53.30% were married couplesliving together, 15.30% had a female householder with no husband present, and 27.20% were non-families. 24.00% of all households were made up of individuals and 10.50% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.12. In the county, the population was spread out with 28.20% under the age of 18, 9.10% from 18 to 24, 27.90% from 25 to 44, 21.80% from 45 to 64, and 13.00% who were 65 years of age or older. The median agewas 34 years. For every 100 females there were 92.10 males. For every 100 females age 18 and over, there were 89.50 males. The median income for a household in the county was $27,582, and the median income for a family was $31,820. Males had a median income of $26,262 versus $19,703 for females. The per capita income for the county was $13,465. About 16.50% of families and 20.70% of the population were below the poverty line, including 27.90% of those under age 18 and 24.40% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 17,212 people, 6,339 households, and 4,594 families living in the county. The population density was. There were 7,287 housing units at an average density of. The racial makeup of the county was 67.0% white, 27.3% black or African American, 0.7% Asian, 0.2% American Indian, 3.4% from other races, and 1.4% from two or more races. Those of Hispanic or Latino origin made up 5.9% of the population. In terms of ancestry, 21.5% were American, 9.9% were Irish, and 5.0% were German. Of the 6,339 households, 38.1% had children under the age of 18 living with them, 49.8% were married couples living together, 16.5% had a female householder with no husband present, 27.5% were non-families, and 23.6% of all households were made up of individuals. The average household size was 2.69 and the average family size was 3.16. The median age was 36.4 years. The median income for a household in the county was $31,390 and the median income for a family was $37,352. Males had a median income of $32,853 versus $25,122 for females. The per capita income for the county was $16,528. About 21.3% of families and 23.3% of the population were below the poverty line, including 29.9% of those under age 18 and 23.3% of those age 65 or over.
