According to the U.S. Census Bureau, the county has a total area of, of which is land and is water. Most of the southern portion of Jenkins County, from southwest of Millen to west of Hiltonia, is located in the Lower Ogeechee River sub-basin of the Ogeechee River basin, with the exception of very small parts of the southwestern corner of the county, north and east of Garfield, which are located in the Canoochee River sub-basin of the same Ogeechee River basin. The northwestern portion of Jenkins County is located in the Upper Ogeechee River sub-basin of the Ogeechee River basin, with just the northeastern corner of the county located in the Brier Creek sub-basin of the Savannah River basin.
As of the census of 2000, there were 8,575 people, 3,214 households, and 2,269 families living in the county. The population density was 24 people per square mile. There were 3,907 housing units at an average density of 11 per square mile. The racial makeup of the county was 56.29% White, 40.49% Black or African American, 0.15% Native American, 0.21% Asian, 0.09% Pacific Islander, 2.06% from other races, and 0.70% from two or more races. 3.35% of the population were Hispanic or Latino of any race. There were 3,214 households out of which 33.70% had children under the age of 18 living with them, 45.90% were married couplesliving together, 19.70% had a female householder with no husband present, and 29.40% were non-families. 25.60% of all households were made up of individuals and 11.30% had someone living alone who was 65 years of age or older. The average household size was 2.63 and the average family size was 3.16. In the county, the population was spread out with 28.50% under the age of 18, 9.20% from 18 to 24, 26.40% from 25 to 44, 22.30% from 45 to 64, and 13.60% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 92.00 males. For every 100 females age 18 and over, there were 86.70 males. The median income for a household in the county was $24,025, and the median income for a family was $29,539. Males had a median income of $28,804 versus $20,252 for females. The per capita income for the county was $13,400. About 22.30% of families and 28.40% of the population were below the poverty line, including 39.60% of those under age 18 and 25.50% of those age 65 or over.
2010 census
As of the 2010 United States Census, there were 8,340 people, 3,192 households, and 2,164 families living in the county. The population density was. There were 4,221 housing units at an average density of. The racial makeup of the county was 54.9% white, 40.5% black or African American, 0.4% Asian, 0.3% American Indian, 2.6% from other races, and 1.2% from two or more races. Those of Hispanic or Latino origin made up 4.0% of the population. In terms of ancestry, 13.0% were American, 10.1% were English, 7.4% were Irish, and 6.3% were German. Of the 3,192 households, 34.7% had children under the age of 18 living with them, 42.1% were married couples living together, 20.3% had a female householder with no husband present, 32.2% were non-families, and 28.7% of all households were made up of individuals. The average household size was 2.59 and the average family size was 3.16. The median age was 38.2 years. The median income for a household in the county was $27,686 and the median income for a family was $35,876. Males had a median income of $36,391 versus $25,814 for females. The per capita income for the county was $17,629. About 17.6% of families and 19.1% of the population were below the poverty line, including 24.1% of those under age 18 and 20.8% of those age 65 or over.
