As of the census of 2000, there were 574,335 people, 212,890 households, and 144,126 families residing in the county. The current estimated population is 604,323. The population density was 671 people per square mile (259/km²). There were 224,000 housing units at an average density of 262 per square mile (101/km²). The racial makeup of the county was 83.13% White, 8.93% Black or African American, 0.52% Native American, 1.86% Asian, 0.06% Pacific Islander, 3.34% from other races, and 2.16% from two or more races. 7.00% of the population were Hispanic or Latino of any race. 19.6% were of Dutch, 14.9% German, 7.6% English, 7.4% Irish, 7.1% Polish and 5.5% American ancestry according to Census 2000. 90.0% spoke English and 6.0% Spanish as their first language.
There were 212,890 households out of which 35.80% had children under the age of 18 living with them, 52.30% were married couples living together, 11.60% had a female householder with no husband present, and 32.30% were non-families. 25.60% of all households were made up of individuals and 8.00% had someone living alone who was 65 years of age or older. The average household size was 2.64 and the average family size was 3.20.
In the county the population was spread out with 28.30% under the age of 18, 10.50% from 18 to 24, 31.20% from 25 to 44, 19.70% from 45 to 64, and 10.40% who were 65 years of age or older. The median age was 32 years. For every 100 females there were 96.90 males. For every 100 females age 18 and over, there were 93.70 males.
The median income for a household in the county was $45,980, and the median income for a family was $54,770. Males had a median income of $39,878 versus $27,364 for females. The per capita income for the county was $21,629. 8.90% of the population and 6.30% of families were below the poverty line. Out of the total people living in poverty, 10.20% are under the age of 18 and 7.50% are 65 or older.