As of the census of 2000, there were 302,963 people, 107,358 households, and 77,619 families residing in the county. The population density was 464 people per square mile (179/km²). There were 118,425 housing units at an average density of 181 per square mile (70/km²). The racial makeup of the county was 55.15% White, 34.90% Black or African American, 1.55% Native American, 1.88% Asian, 0.30% Pacific Islander, 3.13% from other races, and 3.09% from two or more races. 6.90% of the population were Hispanic or Latino of any race.
By 2005 Cumberland County's population was 51.5% non-Hispanic whites. It was 36.7% African-American. 6.4% of the population was Latino. 3.1% of the population reported more than one race. 2.1% of the population was Asian. 1.7% of the population was Native American.
There were 107,358 households out of which 39.40% had children under the age of 18 living with them, 52.90% were married couples living together, 15.50% had a female householder with no husband present, and 27.70% were non-families. 22.40% of all households were made up of individuals and 5.90% had someone living alone who was 65 years of age or older. The average household size was 2.65 and the average family size was 3.11.
In the county the population was spread out with 27.90% under the age of 18, 13.70% from 18 to 24, 32.90% from 25 to 44, 17.80% from 45 to 64, and 7.70% who were 65 years of age or older. The median age was 30 years. For every 100 females there were 102.30 males. For every 100 females age 18 and over, there were 101.90 males.
The median income for a household in the county was $37,466, and the median income for a family was $41,459. Males had a median income of $28,308 versus $22,379 for females. The per capita income for the county was $17,376. About 10.40% of families and 12.80% of the population were below the poverty line, including 16.80% of those under age 18 and 13.70% of those age 65 or over.