It is thought that more than 71% of family carers in Ireland are not registered.
A campaign is being launched today to get people who are caring for family members to say so in the upcoming census.
For the first time carers under the age of 15 can be included in the category.
Frank Goodwin from the Carers Count Campaign says quantifying the number of unpaid carers in Ireland is important for policy makers.
Mr Goodwin said: "Policy is formulated at central government departments, so the department of health and department of social protection will see the figures which the CSO estimates could be as high as 71% of an increase on the 2006 census."