Between 1960 and 1963
When Nigeria was a British protectorate, it was divided into the Southern and Northern regions, after amalgamation in 1912. Nigeria had been divided into 3 regions — Northern, Western and Eastern regions after its independence in 1960.
Between 1963 and 1967
In 1963, the mid-western region was carved out of the Western region, making it four regions in Nigeria.
Between 1967 and 1976
Nigeria had gained independence and survived a coup d’etat, putting Nigeria under military rule. In 1967, General Yakubu Gowon divided the regions were divided into 12 states. This was also the time when the eastern and the mid-western regions unsuccessfully attempted to secede from Nigeria. The states that formed were Northeastern state, Northwestern state, Kano state, Kaduna state, Kwara, Benue-Plateau state, Western state, Lagos, Bendel state, Rivers, Cross River state and East Central state.
The former midwestern region was not divided but rather formed the Bendel state. In February, 1976, the Federal Capital Territory was formed from parts of Benue-Plateau, North-Central and North-Western states or the current Nasarawa, Niger and Kogi states.
Between 1976 and 1987
In 1976, seven new states were created out of the already existing states. The East Central state was divided to Imo and Anambra states. The Western state was divided into Ogun, Oyo and Ondo. Benue-Plateau state was separated to two individual states. North Western state was split into Niger and Sokoto, while the Borno, Bauchi and Gongola were formed out of the North Eastern state.
Between 1987 and 1991
In 1987, two more states were formed to make up 21 states altogether. Akwa-Ibom was carved out of Cross-River and Katsina was carved out of Kaduna.
Between 1991 and 1996
On December 12, 1991, the Federal Capital Territory of Abuja, formerly known as Suleja, was officially announced as Nigeria’s new capital, replacing Lagos. Also during this period, nine more states were added to the list of states in Nigeria. Abia was carved out of Imo, Osun from Oyo and Enugu from Anambra. Bendel state was dissolved to form Edo and Delta states. Kogi was carved out of Benue and Kwara while Jigawa was carved out of Kano. Kebbi was gotten from Sokoto, Yobe from Borno, and Gongola was dissolved to form Adamawa and Taraba.
1996
Six more states were added to the already existing 30 to form a total of 36 states. Ebonyi state was carved out of Abia and Enugu, Bayelsa was carved out Rivers state, Ekiti separated from Ondo, Nasarawa from Plateau, Zamfara from Sokoto and Gombe from Bauchi. These were the last changes made to the state structure of Nigeria and still present till today.