According to the United States Census Bureau, the city has a total area of 7.8 square miles (20.2 km²), of which, 7.6 square miles (19.8 km²) of it is land and 0.1 square miles (0.4 km²) of it (1.80%) is water.
There were 2,035 households out of which 34.3% had children under the age of 18 living with them, 40.2% were married couples living together, 22.1% had a female householder with no husband present, and 33.5% were non-families. 30.2% of all households were made up of individuals and 12.5% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 3.01.
In the city the population was spread out with 28.4% under the age of 18, 8.9% from 18 to 24, 27.6% from 25 to 44, 20.3% from 45 to 64, and 14.8% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 86.8 males. For every 100 females age 18 and over, there were 79.7 males.
The median income for a household in the city was $26,722, and the median income for a family was $37,841. Males had a median income of $35,039 versus $21,912 for females. The per capita income for the city was $17,709. About 20.4% of families and 22.0% of the population were below the poverty line, including 30.5% of those under age 18 and 16.7% of those age 65 or over.
Built in 1832, the South Carolina Railroad connected Charleston to Hamburg on the Savannah River. Hamburg was near Augusta, Georgia. This was the first steam railroad in the world. The railroad went through the middle of the county. Two stops on the railroad created the towns of Blackville, South Carolina and Williston, South Carolina in the mid-nineteenth century.
Built in 1858, the sundial in Barnwell is often thought to be the only remaining vertical freestanding sundial in the USA. It was surrounded by a parking lot in the 1960’s but in the 1990s the Town of Barnwell removed the parking, built a park, and made the sundial a focal point. Another, of more recent construction, exists in front of the Wise County Courthouse in Texas, and there may be more.
Barnwell was hated by General Sherman; he felt that the town should be burnt to the ground since it carried the name of one of the most prominent politicians who had demanded South Carolina’s withdrawal from the Union. When Major Kilpatrick’s cavalry marched through Barnwell, they used the Church of the Holy Apostles, erected in 1856, as a stable for his horses. The hoof prints are still visible in the floors. The medieval font in the church was used to water the horses.
Built of cypress wood from the local swamps, the Church of the Holy Apostles was constructed in 17xx and has been listed on the National Register of Historic Places.
Barnwell County has decreased in size over the years as new counties were created within its boundaries (Aiken in 1871, Bamberg in 1897 and Allendale in 1919).
Several towns and over 100 cemeteries were relocated during this time. Dunbarton and Ellenton are but two. Dunbarton was the town in which Duncannon was located; it was once a sprawling wildlife preserve and early 19th century plantation. Former President George H. W. Bush, with his brothers, used to visit their grandfather George Herbert Walker at the plantation. He and his family spent many Christmases there. Union General William T. Sherman allegedly spared the plantation, built in 1835, because a woman and sick child were resting in a bedroom upstairs
US Army soldiers were brought into the county and were used as guards at this new facility. A camp was constructed for the soldiers off of Clinton Street in an area of the Little Salkehatchie swamp called O’Bannon Point. Most locals call this road “Barracks Road”. After discharge, many of these troops stayed on at SRP as civilian guards.
DuPont ran the Savannah River Site until 1989, when Westinghouse began the management of the facilities for the Department of Energy. The Savannah River Plant changed its name to the Savannah River Site. It was once one of the largest employers in the county.