Charleston, county, southern South Carolina, U.S. It comprises a low-lying coastal region with numerous swamps and marshy areas. A portion of the Sea Islands, strung along the Atlantic coast, form the southeastern border; rivers and the Intracoastal Waterway separate the islands from the mainland. The northern end of this long, narrow county includes Cape Romain National Wildlife Refuge on the Sea Islands and, inland, part of Francis Marion National Forest. In the unique environment of Kiawah Island, which includes salt marshes, woods, and sandy beaches, lives a wide variety of wildlife, including alligators, 140 species of birds, and the endangered Atlantic loggerhead sea turtle. Charles Towne Landing and Hampton Plantation state parks lie within Charleston county.

In 2019, Charleston County, SC had a population of 411k people with a median age of 38.4 and a median household income of $71,531. Between 2018 and 2019 the population of Charleston County, SC grew from 405,905 to 411,406, a 1.36% increase and its median household income grew from $63,459 to $71,531, a 12.7% increase.

95.8% of the residents in Charleston County, SC are U.S. citizens.

The largest universities in Charleston County, SC are College of Charleston (2,637 degrees awarded in 2019), Trident Technical College (2,073 degrees), and Citadel Military College of South Carolina (1,043 degrees).

In 2019, the median property value in Charleston County, SC was $342,500, and the homeownership rate was 63.7%. Most people in Charleston County, SC drove alone to work, and the average commute time was 23 minutes. The average car ownership in Charleston County, SC was 2 cars per household.

Charleston County, SC borders Berkeley County, SC, Colleton County, SC, Dorchester County, SC, and Georgetown County, SC.