date and the month the 1991 population census was taken in nigeria?

Answer 1

SOURCE: 1991 CIA WORLD FACTBOOK
Population: 122,470,574 (July 1991), growth rate 3.0% (1991)
http://www.theodora.com/wfb1991/nigeria/nigeria_people.html


................. Nigeria
.............................Population:
https://www.cia.gov/cia/publications/factbook/geos/ni.html#People
131,859,731
note: estimates for this country explicitly take into account the effects of excess mortality due to AIDS; this can result in lower life expectancy, higher infant mortality and death rates, lower population and growth rates, and changes in the distribution of population by age and sex than would otherwise be expected (July 2006 est.)