Iseyin is a city located in Oyo, Nigeria. It is approximately 100 km (62 mi) north of Ibadan. The city was estimated to have a population of 236,000, according to United Nations 2005 estimate, which increased to 362,990 in 2011, and has a total land mass of 2,341 km2 (904 sq mi). Its inhabitants are mostly of Yoruba origin and its ruler is the Aseyin of Iseyin, with the current being Oba Sefiu Oyebola Adeyeri III, Ajirotutu I.

Oyo State is an inland state in southwestern Nigeria. Its capital is Ibadan, the third most populous city in the country and formerly the second most populous city in Africa. Oyo State is bordered to the north by Kwara State for 337 km, to the east by Osun State for 187 km, partly across the River Osun, and to the south by Ogun State, and to the west by the Republic of Benin for 98 km. With a projected population of 7,976,100 in 2022, Oyo State is the sixth most populous in the Nigeria.