Ascertainment of population
Section 75 · 1999 Constitution (2004 edition)
What Constitution says
For the purposes of section 72 of this Constitution, the number of inhabitants of Nigeria or any part thereof shall be ascertained by reference to the 1991 census of the population of Nigeria or the latest census held in pursuance of an Act of the National Assembly after the coming into force of the provisions of this Part of this Chapter of this Constitution.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 51. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections