Calhoun County is part of the Columbia, South Carolina, Metropolitan Statistical Area.
As of the census of 2000, there were 15,185 people, 5,917 households, and 4,272 families residing in the county. The population density was 40 people per square mile (15/km²). There were 6,864 housing units at an average density of 18 per square mile (7/km²). The racial makeup of the county was 50.03% White, 48.69% Black or African American, 0.19% Native American, 0.14% Asian, 0.03% Pacific Islander, 0.24% from other races, and 0.69% from two or more races. 1.40% of the population were Hispanic or Latino of any race.
There were 5,917 households out of which 30.20% had children under the age of 18 living with them, 52.00% were married couples living together, 15.80% had a female householder with no husband present, and 27.80% were non-families. 24.50% of all households were made up of individuals and 9.60% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.03.
In the county, the population was spread out with 25.10% under the age of 18, 7.40% from 18 to 24, 27.00% from 25 to 44, 26.70% from 45 to 64, and 13.80% who were 65 years of age or older. The median age was 39 years. For every 100 females there were 90.10 males. For every 100 females age 18 and over, there were 86.40 males.
The median income for a household in the county was $32,736, and the median income for a family was $39,823. Males had a median income of $31,431 versus $22,267 for females. The per capita income for the county was $17,446. About 13.20% of families and 16.20% of the population were below the poverty line, including 20.40% of those under age 18 and 18.30% of those age 65 or over.