As of the 2010 census, there were 308,760 people, 109,199 households, and 82,288 families residing in the county. The population density was . There were 116,040 housing units at an average density of . The racial makeup of the county was 90.1% white, 2.5% Asian, 1.1% black or African American, 0.3% American Indian, 4.3% from other races, and 1.7% from two or more races. Those of Hispanic or Latino origin made up 11.4% of the population. In terms of ancestry, 34.4% were of German heritage, 18.7% were of Irish ancestry, 14.2% Polish, 10.8% Italian, 7.8% English, and 3.7% of American heritage.