Mona monkey in the context of Western Africa

Lagos State (Yoruba: Ìpínlẹ̀ Èkó, Gun: Ayìmátẹ̀n Awọnlìn tọ̀n) is a state in southwestern Nigeria. Of the 36 states, Lagos is the most populous state but has the smallest landmass in Nigeria. Bounded to the south by the Bight of Benin and to the west by the international border with the Republic of Benin, Lagos State borders Ogun State to the north and east, making it the only Nigerian state to border only one other state. Named for the city of Lagos — the most populous city in Africa — the state was formed from the Western Region and the former Federal Capital Territory on 27 May 1967.

Geographically, Lagos State is dominated by bodies of water with nearly a quarter of the state's area being lagoons, creeks, and rivers. The largest of these bodies are the Lagos and Lekki lagoons in the state's interior with the Ogun and Osun rivers flowing into them. Many other rivers and creeks flow throughout the state and serve as vital means of transportation for people and goods. On land, non-urbanized areas are within the tropical Nigerian lowland forests ecoregion with natural areas containing threatened populations of mona monkey, tree pangolin, and hooded vulture along with a transitory population of African forest elephants. Offshore, the state is also biodiverse as there are large fish populations along with African manatees and crocodiles.

Ekiti listen(Yoruba: Ìpínlẹ̀ Èkìtì) is a state in southwestern Nigeria, bordered to the North by Kwara State for 61 km, to the Northeast by Kogi State for 92 km, to the South and Southeast by Ondo State, and to the West by Osun State for 84 km. Named for the Ekiti people—the Yoruba subgroup that makes up the majority of the state's population—Ekiti State was carved out from a part of Ondo State in 1996 and has its capital as the city of Ado-Ekiti.

One of the smallest and most educated states with the highest number of professors in Nigeria, Ekiti is the 31st largest in the area and 30th most populous with an estimated population of nearly 3.5 million as of 2022. Geographically, the state is divided between the Nigerian lowland forests in most of the state and the drier Guinean forest–savanna mosaic in the north. Among the state's nature are false acraeas, mona monkey, forest buffalo, and grey parrot populations along with one of the last remaining Nigeria-Cameroon chimpanzee populations with a troop of about 20 chimpanzees in the heavily threatened Ise Forest Reserve. In March 2022, Ekiti State became the first state in Nigeria to adopt a state tree as one of its official symbols. On World Forest Day 2022, Governor Kayode Fayemi announced that Obeche (Triplochiton scleroxylon) had been chosen as State Tree owing to its local prominence and environmental, economic and cultural significance.

OsunListen (/ˈoʊʃuːn/ OH-shoon; Yoruba: Ìpínlẹ̀ Ọ̀ṣun [ìk͡pĩ́lɛ̀ ɔ̀ʃũ̄]), is a state in southwestern Nigeria; bounded to the east by Ekiti and Ondo states for 84 km and for 78 km respectively, to the north by Kwara State for 73 km, to the south by Ogun State for 84 km and to the west by Oyo State, mostly across the River Osun. Named for the River Osun—a vital river which flows through the state—the state was formed from the southeast of Oyo State on 27 August 1991 and has its capital as the city of Osogbo.

Of the 36 states of Nigeria, Osun is the ninth smallest in area and 25th most populous state with an estimated population of about 4.7 million as of 2016. Geographically, the state is divided between the Nigerian lowland forests in most of the state and the drier Guinean forest–savanna mosaic in the north. The major geographical features are rivers including the state's namesake, the River Osun which bisects the state's interior before forming much of the state's southwestern border with Oyo State and flowing south. Other important rivers are the Erinle and Oba rivers, both Osun tributaries which flow from the north before meeting the Osun along the southwestern border. Among the state's fauna are mona monkey, common kestrel, purple heron, and royal antelope, along with some of Nigeria's last remaining Nigeria-Cameroon chimpanzee and African forest elephant which inhabit the heavily threatened forests along the southern borders with Ondo and Ogun states.