On November 6, 1977, the Kelly Barnes Dam collapsed after a period of heavy rainfall, and the resulting flood killed 39 people and caused $2.8 million in damage.
According to the U.S. Census Bureau, the county has a total area of 184 square miles (480 km2), of which 179 square miles (460 km2) is land and 5.1 square miles (13 km2) (2.8%) is water.
The northern half of Stephens County is located in the Tugaloo River sub-basin of the Savannah River basin, while the southern half of the county is located in the Broad River sub-basin of the same Savannah River basin.
As of the 2010 United States Census, there were 26,175 people, 10,289 households, and 7,236 families residing in the county. The population density was 146.1 inhabitants per square mile (56.4/km2). There were 12,662 housing units at an average density of 70.7 per square mile (27.3/km2). The racial makeup of the county was 85.1% white, 10.9% black or African American, 0.7% Asian, 0.3% American Indian, 0.1% Pacific islander, 1.0% from other races, and 2.0% from two or more races. Those of Hispanic or Latino origin made up 2.4% of the population. In terms of ancestry, 14.7% were American, 9.1% were Irish, 8.1% were German, and 7.4% were English.
Of the 10,289 households, 31.5% had children under the age of 18 living with them, 52.8% were married couples living together, 13.2% had a female householder with no husband present, 29.7% were non-families, and 25.7% of all households were made up of individuals. The average household size was 2.49 and the average family size was 2.96. The median age was 40.7 years.
The median income for a household in the county was $34,938 and the median income for a family was $41,768. Males had a median income of $35,814 versus $24,834 for females. The per capita income for the county was $18,285. About 12.3% of families and 18.8% of the population were below the poverty line, including 25.9% of those under age 18 and 16.0% of those age 65 or over.