National protected areas

• Francis Marion National Forest (part)
• Hell Hole Bay Wilderness
• Wambaw Creek Wilderness (part)

State and local protected areas/sites

• Bonneau Ferry Wildlife Management Area^[7]
• Canal Wildlife Management Area^[7]
• Childsbury Towne Heritage Preserve^[7]
• Cypress Gardens
• Hatchery Wildlife Management Area^[7]
• Moultrie Hunt Unit Wildlife Management Area^[7]
• Old Santee Canal Park
• Site of Francis Marion Tomb
• Wee Tee Wildlife Management Area (part)

Major water bodies

• Cooper River
• Goose Creek Reservoir
• Lake Marion
• Lake Moultrie
• Santee River
• Wambaw Creek
• Wando River

Adjacent counties

• Georgetown County – east
• Williamsburg County – northeast
• Clarendon County – north
• Orangeburg County – northwest
• Dorchester County – west
• Charleston County – south

Major highways

• I-26
• I-526
• 
  US 17 Alt.
• 
  US 17 Alt. Truck
• US 52
• US 176
• SC 6
• 
  SC 6 Truck
• SC 16
• SC 27
• SC 41
• SC 45
• SC 165
• SC 311
• SC 402

Major infrastructure

• Seed Orchard Helibase

2020 census

As of the 2020 census, there were 229,861 people, 80,640 households, and 57,117 families residing in the county.

2010 census

At the 2010 census, there were 177,843 people, 65,419 households, and 47,141 families living in the county.^[14][12] The population density was 161.8 inhabitants per square mile (62.5/km²). There were 73,372 housing units at an average density of 66.8 per square mile (25.8/km²).^[15] The racial makeup of the county was 66.5% white, 25.0% black or African American, 2.3% Asian, 0.6% American Indian, 0.1% Pacific islander, 2.8% from other races, and 2.7% from two or more races. Those of Hispanic or Latino origin made up 6.0% of the population.^[14][16]

Of the 65,419 households, 38.0% had children under the age of 18 living with them, 51.3% were married couples living together, 15.3% had a female householder with no husband present, 27.9% were non-families, and 22.0% of households were made up of individuals. The average household size was 2.66 and the average family size was 3.10. The median age was 34.5 years.^[14]

The median household income was $50,777 and the median family income was $56,869. Males had a median income of $40,534 versus $30,997 for females. The per capita income for the county was $22,865. About 9.9% of families and 12.6% of the population were below the poverty line, including 18.2% of those under age 18 and 10.3% of those age 65 or over.^[17]

2000 census

At the 2000 census, there were 142,651 people, 49,922 households, and 37,691 families living in the county. The population density was 130 people per square mile (50 people/km²). There were 54,717 housing units at an average density of 50 per square mile (19/km²). The racial makeup of the county was 68.00% White, 26.63% Black or African American, 0.52% Native American, 1.87% Asian, 0.08% Pacific Islander, 1.20% from other races, and 1.70% from two or more races. 2.76% of the population were Hispanic or Latino of any race. 16.4% were of American, 10.0% German, 8.4% Irish and 7.7% English ancestry according to Census 2000.^[18] Of the 49,922 households 39.20% had children under the age of 18 living with them, 56.70% were married couples living together, 14.20% had a female householder with no husband present, and 24.50% were non-families. 19.40% of households were one person and 5.60% were one person aged 65 or older. The average household size was 2.75 and the average family size was 3.15.

The age distribution was 28.00% under the age of 18, 11.70% from 18 to 24, 31.20% from 25 to 44, 21.20% from 45 to 64, and 7.90% 65 or older. The median age was 32 years. For every 100 females, there were 103.20 males. For every 100 females age 18 and over, there were 102.20 males.

The median household income was $39,908 and the median family income was $44,242. Males had a median income of $31,583 versus $22,420 for females. The per capita income for the county was $16,879. About 9.70% of families and 11.80% of the population were below the poverty line, including 15.60% of those under age 18 and 12.90% of those age 65 or over.

Cities

• Charleston (mostly in Charleston County)
• Goose Creek (largest community)
• Hanahan
• North Charleston (partly in Dorchester County and Charleston County)

Towns

• Bonneau
• Jamestown
• Moncks Corner (county seat)
• St. Stephen
• Summerville (partly in Dorchester County and Charleston County)

Census-designated places

• Bonneau Beach
• Ladson (partly in Charleston County and Dorchester County)
• Pimlico
• Pinopolis
• Russellville
• Sangaree

Unincorporated communities

• Bethera
• Cross
• Gumville
• Huger
• Pineville
• Pringletown
• Cane Bay