Nigeria Facts for Kids The official name of Nigeria is the Federal Republic of Nigeria. Nigeria is located in West Africa, it shares a land boarder with Benin, Chad, Cameroon, and Niger. The total land mass of Nigeria is 923,768 km² (356,669 mi²), which makes it the world's 32nd-largest country by land mass. The British colonised Nigeria in the late 19th century through to 1960 when Nigeria became independent. Nigeria is a member of both the British Commonwealth and the African Union. Nigeria has a population of nearly 175 million people (174,507,539) as of July 2013, making it the most populous country in Africa, and the 7th most populous country in the world. The largest city in Nigeria is Lagos with an estimated population of around 21 million people. The capital city is of Nigeria is Abuja, which was planned out and then built in the 1980s, officially replacing Lagos as the capital in 1991. Nigeria has over 250 ethnic groups, th...