Married-couple families accounted for 73.9% of the 3,422,300 census families in Ontario, the highest proportion in the country. On the other hand, common-law families represented only 10.3% of all census families, the lowest proportion. Lone-parent families accounted for 15.8% of families.
Census families in Ontario grew 7.2% between 2001 and 2006, a slightly faster gain than the national average of 6.3%. The number of common-law-couple families grew most quickly during the intercensal period (+17.6%). Lone-parent families rose 11.2% and the number of married-couple families was up only 5.2%.
The 2006 Census counted 17,500 same-sex couples in Ontario, representing 0.6% of all couples in the province, on par with the national average. Of all same-sex couples in Canada, 38.6% lived in Ontario.
Ontario became the first province to legalize same-sex marriage in June 2003. Over one-fifth (21.5%) of same-sex couples in this province were married, well above the national average of 16.5%.
The census enumerated 4,555,000 private households in Ontario in 2006, up 8.0% from 2001. The population in private households increased 6.5%. Many of these households were large—10.5% consisted of five or more persons—compared to the national average of 8.7%. About one-quarter (24.3%) of households were comprised of only one person.
Ontario was one of only two provinces in which the proportion of households with couples and children still exceeded the proportion of households comprised of couples without children. About 31.2% of all households consisted of couples with children in 2006, compared to 28.3% which had none. Alberta was the only other province in this situation. One reason for this may be that Ontario is the second youngest province in Canada, after Alberta. In addition, many immigrants are women of childbearing age, who have higher numbers of children on average.
Ontario also had one of the highest proportions of young adults aged 20 to 29 living in the parental home, second only to Newfoundland and Labrador. In 2006, 51.5% of young adults in this age group lived at home with their parents, up from 47.1% in 2001, and well above the national average of 43.5%. In Newfoundland and Labrador, 52.2% of young adults lived at home.
Young adults could be living at home because of the higher cost of living in some large urban areas of Ontario, such as Toronto.