As a best practice, Contacts should have a Household record. In fact, Contacts without Households are considered a data quality issue.
The Customer Portal Report Card awards an A grade when less than 2% of your Contacts have also had activity in the Activity Log within the last 365 days.
This tool has a Create Missing Records option. Click here for more information on the Transfer Selection tool.
Views and Notifications can be created to find and remedy these Contact records.
Ensure to always use a tool to create new records - all of these tools will create the Contact & Household record:
Ensure that when you remove a person from a Household (such as in the case of divorce) you use the transfer selection tool to create a Household for this individual. This can be done even if you do not have a new address for this individual.