Nigeria is the most populous country in Africa but exactly how populous is a subject of speculation. The United Nations estimates that the population in 2004 was at 131,530,000,[54] with the population distributed as 51.7% rural and 48.3% urban, and with a population density of 139 people per square kilometer. The results of the most recent census were released in December 2006 and gave a population of 140,003,542.

According to the United Nations, Nigeria has been undergoing explosive population growth and one of the highest growth and fertility rates in the world. By their projections, Nigeria will be one of the countries in the world that will account for most of the world's total population increase by 2050. According to current data, one out of every four Africans is Nigerian.

Education is also in a state of neglect. After the 1970s oil boom, tertiary education was improved so that it would reach every subregion of Nigeria. Education is provided free by the government, but the attendance rate for secondary education is only 29% (32% for males, 27% for females). The education system has been described as "dysfunctional" largely due to decaying institutional infrastructure. 68% of the population is literate, and the rate for men (75.7%) is higher than that for women (60.6%).

Ethno-linguistic groups
Nigeria has more than 250 ethnic groups, with varying languages and customs, creating a country of rich ethnic diversity. The largest ethnic groups are the Fulani/Hausa, Yoruba, Igbo, accounting for 68% of population, while the Edo, Ijaw, Kanuri, Ibibio, Ebira Nupe and Tiv comprise 27%; other minorities make up the remaining 7 percent. The middle belt of Nigeria is known for its diversity of ethnic groups, including the Pyem, Goemai, and Kofyar.

There are small minorities of British, Americans, East Indians, Chinese (est. 50,000), white Zimbabweans, Japanese, Syrian, Lebanese and refugees and immigrants from other West African or East African nations. These minorities mostly reside in major cities such as Lagos and Abuja, or in the Niger Delta as employees for the major oil companies. A number of Cubans settled Nigeria as political refugees following the Cuban Revolution.

In the middle of the nineteenth century, a number of ex-slaves of Afro-Cuban and Afro-Brazilian descent and emigrants from Sierra Leone established communities in Lagos, Ibadan and other regions of Nigeria. Many ex-slaves came to Nigeria following the emancipation of slaves in Latin America. Many of the immigrants, sometimes called Saros (immigrants from Sierra Leone) and Amaro (ex-slaves from Brazil) later became prominent merchants and missionaries in Lagos and Abeokuta.