The Central Statistics Office has moved to reassure those who have not yet received a Census form that deliveries are continuing, saying it is "likely" that some households will receive a form after 3 April.
The CSO said while the delivery of forms has progressed well, a "small number" of homes will end up having to complete it retrospectively.
It added that, as with previous Censuses, deliveries of forms to certain areas has been "challenging".
These include Dublin and Limerick city centres, as well as parts of Donegal and Waterford.
It also highlighted that areas with a high density of apartment buildings can be problematic, adding that Covid-19 has lead to some enumerators having to isolate.
Census forms were sent out to households from early last month, with 1.8 million of them delivered as of midnight last night. The CSO said this accounts for 95% of households in the country.
Households that have not yet received a form, or been contacted by an enumerator, are being urged to contact the CSO to request a form.
The helpdesk, which can be contacted at 0818 2022 04, will operate between 11am and 6pm this Saturday and Sunday.
"In recent days, a number of enumerators have been reallocated to areas where further deliveries are still required," said Head of Census Administration Eileen Murphy.
She added: "Enumerators will now also post forms into homes where they have been unable to make personal contact.
"All of these efforts will ensure only a very small number of households will not have a census form on Census night. This is nothing to be concerned about and has occurred with previous censuses."
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Census Q&A: Can I do it online?
This year's Census will include a time capsule to "send a message to the future". The forms will be protected for 100 years after which they will be published and publicly available.
Former Head of Special Projects at the National Archives of Ireland Catriona Crowe said this Census includes questions about internet access and house size, all which will be "fascinating" for descendants.
Speaking on RTÉ’s Morning Ireland, she said they will also be able to read how people are feeling right now.
