There were 458,057 households at the 2010 census, out of which 29.1% had children under the age of 18 living with them, 36.1% were headed by married couples living together, 16.0% had a female householder with no husband present, and 42.0% were classified as non-family households. 33.7% of all households had one or more people under 18 years of age, and 17.6% had one or more people who were 65 years of age or older. The average household size was 2.57 and the average family size was 3.42.. which household was least common?