The Central Statistics Office (CSO) has advised households that did not receive a census form in time for Sunday night that it is not too late to fill one out.
While officials estimate most households received a form ahead of census night, it has been receiving up to 1,500 calls a day from households who said they had not yet received a form.
Additional forms are being distributed to households through local census enumerators.
A spokesman said any household that received the form late should fill it in as they would have if it was delivered in time for Sunday night.
Differing working patterns as well as the rise in gated communities and apartment complexes have contributed to difficulties in delivering 1.5 million census forms over the last few weeks.
Anyone without a form has been asked to contact the CSO's special census phone line, 1890 236 787, available from Monday to Friday, 8am to 8pm.
The 4,500 census enumerators employed by the CSO began the three-week process of collecting forms yesterday. They are starting with institutions such as hotels and hospitals before moving on to households.
Preliminary estimates are expected to be available by July. CSO officials expect the overall population in this census may reach 4.2 million, the highest in 135 years. The number of foreign nationals is expected to be around 10 per cent.