According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. The vast majority of Atkinson County is located in the Satilla River sub-basin of the St. Marys-Satilla River basin. The entire narrow western border area, in a line parallel to the western border and running through Willacoochee, is located in the Alapaha River sub-basin of the Suwannee River basin. A small southeastern corner of the county is located in the Upper Suwannee River sub-basin of the same Suwannee River basin.
As of the census of 2000, there were 7,609 people, 2,717 households, and 1,980 families living in the county. The population density was 22 people per square mile. There were 3,171 housing units at an average density of 9 per square mile. The racial makeup of the county was 66.79% White, 19.61% Black or African American, 0.37% Native American, 0.12% Asian, 0.03% Pacific Islander, 12.03% from other races, and 1.06% from two or more races. 16.95% of the population were Hispanic or Latino of any race. There were 2,717 households out of which 38.80% had children under the age of 18 living with them, 55.10% were married couplesliving together, 12.80% had a female householder with no husband present, and 27.10% were non-families. 23.30% of all households were made up of individuals and 9.10% had someone living alone who was 65 years of age or older. The average household size was 2.78 and the average family size was 3.27. In the county the population was spread out with 30.30% under the age of 18, 10.90% from 18 to 24, 29.60% from 25 to 44, 19.90% from 45 to 64, and 9.30% who were 65 years of age or older. The median age was 31 years. For every 100 females there were 98.00 males. For every 100 females age 18 and over, there were 97.40 males. The median income for a household in the county was $26,470, and the median income for a family was $32,688. Males had a median income of $24,763 versus $18,434 for females. The per capita income for the county was $12,178. About 18.10% of families and 23.00% of the population were below the poverty line, including 27.10% of those under age 18 and 31.00% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 8,375 people, 2,983 households, and 2,159 families living in the county. The population density was. There were 3,522 housing units at an average density of. The racial makeup of the county was 62.2% white, 17.3% black or African American, 0.6% American Indian, 0.3% Pacific islander, 0.3% Asian, 17.7% from other races, and 1.6% from two or more races. Those of Hispanic or Latino origin made up 24.3% of the population. In terms of ancestry, 16.1% were English, 16.0% were Irish, and 7.5% were American. Of the 2,983 households, 41.2% had children under the age of 18 living with them, 50.3% were married couples living together, 15.3% had a female householder with no husband present, 27.6% were non-families, and 22.9% of all households were made up of individuals. The average household size was 2.80 and the average family size was 3.29. The median age was 33.4 years. The median income for a household in the county was $33,834 and the median income for a family was $34,859. Males had a median income of $29,286 versus $25,705 for females. The per capita income for the county was $15,456. About 19.8% of families and 28.0% of the population were below the poverty line, including 42.4% of those under age 18 and 21.3% of those age 65 or over.
