National protected area

• Ernest F. Hollings ACE Basin National Wildlife Refuge (part)

State and local protected areas

• Hamilton Ridge Wildlife Management Area^[5]
• James W Webb Wildlife Center and Game Management Area^[6]
• Lake Warren State Park
• Palachucola Wildlife Management Area^[5]
• Webb Wildlife Center^[5]

Major water bodies

• Coosawhatchie River
• Lake George Warren
• Little Salkehatchie River
• Salkehatchie River
• Savannah River

Adjacent counties

• Bamberg County – north
• Colleton County – east
• Beaufort County – southeast
• Jasper County – south
• Effingham County, Georgia – southwest
• Screven County, Georgia – west
• Allendale County – northwest

Major highways

• I-95
• US 21
• 
  US 17 Alt.
• US 278
• US 321
• US 601
• SC 3
• SC 63
• SC 68
• SC 333
• SC 363

Major infrastructure

• Yemassee Station

2020 census

As of the 2020 census, there were 18,561 people, 6,993 households, and 4,148 families residing in the county.

2010 census

At the 2010 census, there were 21,090 people, 7,598 households, and 5,211 families living in the county.^[13][11] The population density was 37.7 inhabitants per square mile (14.6/km²). There were 9,140 housing units at an average density of 16.3 per square mile (6.3/km²).^[14] The racial makeup of the county was 53.9% black or African American, 42.7% white, 0.5% Asian, 0.3% American Indian, 1.3% from other races, and 1.3% from two or more races. Those of Hispanic or Latino origin made up 3.5% of the population.^[13] In terms of ancestry, 6.4% were Irish, 6.3% were American, 5.6% were German, and 5.3% were English.^[15]

Of the 7,598 households, 35.8% had children under the age of 18 living with them, 44.0% were married couples living together, 19.1% had a female householder with no husband present, 31.4% were non-families, and 28.1% of all households were made up of individuals. The average household size was 2.57 and the average family size was 3.15. The median age was 38.4 years.^[13]

The median income for a household in the county was $34,846 and the median income for a family was $43,234. Males had a median income of $31,935 versus $26,826 for females. The per capita income for the county was $16,262. About 17.2% of families and 20.8% of the population were below the poverty line, including 27.9% of those under age 18 and 19.7% of those age 65 or over.^[16]

2000 census

At the 2000 census,^[17] there were 21,386 people, 7,444 households, and 5,315 families living in the county. The population density was 38 people per square mile (15 people/km²). There were 8,582 housing units at an average density of 15 per square mile (5.8/km²). The racial makeup of the county was 55.67% Black or African American, 42.89% White, 0.20% Native American, 0.17% Asian, 0.01% Pacific Islander, 0.62% from other races, and 0.43% from two or more races. 2.56% of the population were Hispanic or Latino of any race.

There were 7,444 households, out of which 34.60% had children under the age of 18 living with them, 47.90% were married couples living together, 18.80% had a female householder with no husband present, and 28.60% were non-families. 25.80% of all households were made up of individuals, and 11.20% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.19.

In the county, the population was spread out, with 27.60% under the age of 18, 8.50% from 18 to 24, 29.70% from 25 to 44, 22.10% from 45 to 64, and 12.10% who were 65 years of age or older. The median age was 35 years. For every 100 females there were 103.80 males. For every 100 females age 18 and over, there were 103.90 males.

The median income for a household in the county was $28,771, and the median income for a family was $34,559. Males had a median income of $29,440 versus $20,418 for females. The per capita income for the county was $13,129. About 17.80% of families and 21.80% of the population were below the poverty line, including 27.60% of those under age 18 and 21.70% of those age 65 or over.

Towns

Unincorporated communities

• Crocketville
• Lena
• McPhersonville
• Nixville