Charleston County is part of the Charleston–North Charleston–Summerville Metropolitan Statistical Area.
As of the census of 2000, there were 309,969 people, 143,326 households, and 97,448 families residing in the county. The population density was 338 people per square mile (130/km²). There were 141,031 housing units at an average density of 154 per square mile (59/km²). The racial makeup of the county was 61.9% White, 34.5% Black or African American, 0.26% Native American, 1.12% Asian, 0.06% Pacific Islander, 0.99% from other races, and 1.16% from two or more races. 2.40% of the population were Hispanic or Latino of any race. 9.6% were of American, 9.5% English, 9.1% German and 7.6% Irish ancestry according to Census 2000.
There were 123,326 households out of which 28.70% had children under the age of 18 living with them, 43.20% were married couples living together, 15.90% had a female householder with no husband present, and 37.20% were non-families. 28.30% of all households were made up of individuals and 8.10% 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 county, the population was spread out with 23.70% under the age of 18, 12.00% from 18 to 24, 30.30% from 25 to 44, 22.00% from 45 to 64, and 11.90% who were 65 years of age or older. The median age was 34 years. For every 100 females there were 93.50 males. For every 100 females age 18 and over, there were 90.50 males.
The median income for a household in the county is $37,810, and the median income for a family was $47,139. Males had a median income of $32,681 versus $25,530 for females. The per capita income for the county was $21,393. About 12.40% of families and 16.40% of the population were below the poverty line, including 22.90% of those under age 18 and 12.70% of those age 65 or over.
In the 2000 census, the county population was classified as about 86% urban. The Charleston-North Charleston Metropolitan Statistical Area includes the populations of Charleston, Berkeley, and Dorchester counties.