There were 19,707 households of which 31.0% had children under the age of 18 living with them, 51.6% were Marriage living together, 10.0% had a female householder with no husband present, 4.2% had a male householder with no wife present, and 34.2% were non-families. 28.2% of all households were made up of individuals and 10.1% had someone living alone who was 65 years of age or older. The average household size was 2.42 and the average family size was 2.97.. which household was least common?