Iseyin is a town located in Oyo State, Nigeria. It is situated approximately 100 km (62 mi) north of Ibadan and covers a total land mass of 2,341 km2 (904 sq mi).
The population of the town was estimated at 236,000 in 2005 and grew to 362,990 by 2011. The inhabitants are primarily of Yoruba origin. The town is governed by the Aseyin of Iseyin; the current ruler is Oba Sefiu Oyebola Adeyeri III, Ajirotutu I.