As of the 2000 census, there are 660,486 people in the county, organized into 272,098 households and 152,102 families. The population density is 1,518 people per square mile (586/km²). There are 288,561 housing units at an average density of 663 per square mile (256/km²). The racial makeup of the county is 79.16% White, 5.70% Asian, 5.67% Black or African American, 1.03% Native American, 0.35% Pacific Islander, 4.03% from other races, and 4.07% from two or more races. 7.51% of the population are Hispanic or Latino of any race. 16.0% were of German, 9.0% English, 8.8% Irish and 5.1% American ancestry according to Census 2000. 83.5% spoke English, 6.3% Spanish, 1.7% Vietnamese and 1.3% Russian as their first language.
There are 272,098 households out of which 26.5% have children under the age of 18 living with them, 40.9% are married couples living together, 10.8% have a female householder with no husband present, and 44.1% are non-families. 32.5% of all households are made up of individuals and 8.6% have someone living alone who is 65 years of age or older. The average household size is 2.37 and the average family size is 3.03.
In the county, the population is spread out with 22.30% under the age of 18, 10.30% from 18 to 24, 33.80% from 25 to 44, 22.50% from 45 to 64, and 11.10% who are 65 years of age or older. The median age is 35 years. For every 100 females there are 98.00 males. For every 100 females age 18 and over, there are 96.10 males.
The median income for a household in the county is $41,278, and the median income for a family is $51,118. Males have a median income of $36,036 versus $29,337 for females. The per capita income for the county is $22,606. 12.70% of the population and 8.20% of families are below the poverty line. Out of the total population, 15.40% of those under the age of 18 and 9.80% of those 65 and older are living below the poverty line.