> The Democratic Republic of the Congo, which by most estimates has the fourth-largest population in Africa, has not conducted a census since 1984. Neither South Sudan nor Eritrea, two of the newest states in Africa (one created in 2011 and the other in 1991), has conducted a census in their entire history as independent states. Afghanistan has not had one since 1979; Chad since 1991; Somalia since 1975.
>>simonw+(OP)
Two countries, ranking 32nd and 41st in Africa have not had a census. Those others have had old census conducted: so we have "some idea" of their population.