As of the census of 2000, there were 534,678 people, 205,411 households, and 140,706 families residing in the county. The population density was 371/km (962/mi²). There were 216,918 housing units at an average density of 151/km²(390/mi²). The racial makeup of the county was 90.98% White, 2.03% Black or African American, 0.24% Native American, 1.26% Asian, 0.03% Pacific Islander, 3.12% from other races, and 2.34% from two or more races. 3.60% of the population were Hispanic or Latino of any race.

There were 205,411 households out of which 33.00% had children under the age of 18 living with them, 51.60% were married couples living together, 13.00% had a female householder with no husband present, and 31.50% were non-families. 26.50% of all households were made up of individuals and 11.00% had someone living alone who was 65 years of age or older. The average household size was 2.54 and the average family size was 3.08.

In the county the population was spread out with 24.60% under the age of 18, 8.50% from 18 to 24, 30.50% from 25 to 44, 22.20% from 45 to 64, and 14.10% who were 65 years of age or older. The median age was 37 years. For every 100 females there were 92.40 males. For every 100 females age 18 and over, there were 88.50 males.

The median income for a household in the county was $43,496, and the median income for a family was $53,733. Males had a median income of $39,361 versus $27,516 for females. The per capita income for the county was $20,978. About 7.80% of families and 10.00% of the population were below the poverty line, including 13.00% of those under age 18 and 12.00% of those age 65 or over.