High Quality Content by WIKIPEDIA articles! As of the census of 2000, there were 1,517,550 people, 590,071 households, and 352,272 families residing in the city of Philadelphia, Pennsylvania. The population density was 4,337.3/km². There were 661,958 housing units at an average density of 1,891.9/km2. Of the 590,071 households, 27.6% had children under the age of 18 living with them, 32.1% were married couples living together, 22.3% had a female householder with no husband present, and 40.3% were non-families. 33.8% of all households were made up of individuals and 11.9% had someone living alone who was 65 years of age or older. The average household size was 2.48 and the average family size was 3.22.