As of the census of 2000, there were 395,357 people, 149,556 households, and 101,997 families residing in the county. The population density was 480 people per square mile (186/km²). There were 162,803 housing units at an average density of 206 per square mile (80/km²). The racial makeup of the county was 77.53% White, 18.30% Black or African American, 0.19% Native American, 1.38% Asian, 0.05% Pacific Islander, 1.42% from other races, and 1.14% from two or more races. Hispanic or Latino of any race were 3.76% of the population. 19.6% were of American, 10.8% English, 9.2% German and 8.9% Irish ancestry according to Census 2000. 93.2% spoke English and 3.9% Spanish as their first language.
There were 149,556 households out of which 31.90% had children under the age of 18 living with them, 52.30% were married couples living together, 12.30% had a female householder with no husband present, and 31.80% were non-families. 26.80% of all households were made up of individuals and 8.50% had someone living alone who is 65 years of age or older. The average household size was 2.47 and the average family size was 3.00.
In the county the population was spread out with 24.60% of the population was under the age of 18, 9.60% from 18 to 24, 31.20% from 25 to 44, 22.80% from 45 to 64, and 11.70% who are 65 years of age or older. The median age was 36 years. For every 100 females, there were 94.80 males. For every 100 females age 18 and over, there were 91.60 males.
The median income for a household in the county was $41,149, and the median income for a family was $50,332. Males had a median income of $37,313 versus $26,034 for females. The per capita income for the county was $22,081. About 7.90% of families and 10.50% of the population were below the poverty line, including 13.20% of those under the age of 18 and 10.60% of those 65 and older.