The Central Statistics Office (CSO) has set up a helpline for householders still without a form for census night tomorrow.
Staff will be on stand-by to take calls on Lo-call 1890 28 04 02 during office hours today and tomorrow, and the local enumerator will be alerted.
The CSO said people without forms need not worry about being left out.
"All of the forms are supposed to have been delivered by now but if for any reason somebody hasn't got one, if they let us know, we'll get one to them as soon as possible," said statistician Mr Francis McCann. "It might be Monday but that's all right. Their answers will still be included."
The number of households in the State is thought to be around 1.4 million. Some 1.75 million census forms have been printed to allow for a margin of error.
Collection of completed forms will start on Monday, beginning with hotels and guesthouses which have the task of recording every guest who stayed the night before.
Guests will also be issued with a short version of the form which records their personal details but excludes housing questions. Anyone spending Sunday night in a hotel but who may have filled in a census form at home beforehand is being asked to make known to the census collector that they are recorded twice.
Collection of forms by the 4,000 enumerators is expected to take a month, and by early June all forms will be transferred to a specially-created census-processing depot in Swords, Co Dublin.
"They will be scanned into computers here so that all the information from the tick boxes can be coded and arranged in a way that we can carry out detailed analysis," Mr McCann said.
The work of the Swords depot is expected to be finished by June of next year, but it will take longer for detailed statistics to emerge. However, provisional population totals should be available this summer.
Forecasters expect the population in this census will reach 3.9 million, the largest since 1871.
The census usually takes place at five-year intervals but was postponed last year because of the foot-and-mouth outbreak. The next one is scheduled for four years' time for easier comparisons with previous decades.
Several new questions have been included in the questionnaire this time, covering nationality, disability, membership of the Travelling community, PC ownership, Internet access, third-level qualifications and time taken to travel to work, school or college.
Mr McCann stressed that all information would be treated confidentially.
Enumerators are bound by the Official Secrets Act and can be fined up to €25,000 if found to have abused information.