Tonight is Census Night, when every person in the country is asked to fill out their census form.
People are being asked to answer the 35 questions wherever they are, and wherever they are from.
A number of groups are reminding people the information is used for planning things like what schools to build and who should control them.
Anyone who fails to take part in the census could face prosecution.
Deirdre Cullen of the CSO has said homeless people will be accounted for.
“So the way we enumerate homeless people is, it’s generally based on where they are on Census Night,” said Cullen.
“Most accommodation for homeless people is dedicated homeless accommodation, we’ve indentified that accommodation and we can classify those people as homeless.
“Then the service providers, Simon (Communities Ireland) and Focus (Ireland), will do a rough sleeper count for us not only in Dublin city, but in Cork and Galway. Then we’ll work with them to gather census information from that rough sleeper count.”