The streets of Nigeria's main cities are quiet, as people have been told to stay at home and wait to be counted in the first census for 15 years.
The headcount is sensitive, as funding and political representation depend on the results but questions of religion and ethnicity have been left out.
There is frustration in many places that the process has started slowly.
Nigeria's president has stressed that the five-day census is not political and urged people to remain calm.
Nigeria is Africa's most populous country but estimates of its population range from 120 to 150 million