Ogun State (Yoruba: Ìpínlẹ̀ Ògùn [ìk͡pĩ́lɛ̀ ògũ̀]) is a state in southwestern Nigeria. It is bordered to the south by Lagos State and the Bight of Benin, to the east by Ondo State, and to the north by Oyo and Osun states while its western border forms part of the national border with the Republic of Benin. The capital and largest city is Abeokuta, and the state is divided into 20 local government areas.
Of the 36 states in the country, Ogun is the 24th largest in area but among the top fifteen most populous, with an estimated population of about 6.4 million as of 2020. Geographically, the state lies primarily in the tropical Nigerian lowland forests ecoregion, although parts of the state's north transition into the Guinean forest–savanna mosaic and some of the coastal south reach the Central African mangrove ecoregion. The Ogun and Yewa rivers are the state's major waterways while the Omo Forest Reserve in the southeastern part of the state is one of the most important conservation areas in the country—home to a variety of bird species along with some of Nigeria's last remaining Nigeria-Cameroon chimpanzee and African forest elephant populations.