Census forms that have been distributed across the country are expected to be filled out tonight.
Every person must, by law, be entered on a form.
The Census was due to be undertaken last year but was postponed because of the Covid-19 pandemic.
It is to record the people staying at a particular address between the hours of 9pm tonight and 7am tomorrow morning.
Enumerators have delivered forms to more than two million homes, hotels, institutions and other accommodation in recent weeks to ensure the information of everyone in the country is captured.
The Central Statistics Office has said a number of households may not have received a census yet and if that is the case they can contact the CSO and retrospectively fill a form in the coming days.
Enumerators will return to collect completed census forms starting on 4 April and no later than 6 May.
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