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.

Ibadan is the capital and most populous city of Oyo State, in Nigeria. It is the third-largest city by population in Nigeria after Lagos and Kano, with a total population of 2,649,000 as of 2021, and over 3 million people within its metropolitan area. It is one of the country's largest cities by geographical area. At the time of Nigeria's independence in 1960, Ibadan was the largest and most populous city in the country, and the second-most populous in Africa behind Cairo. Ibadan is ranked one of the fastest-growing cities in sub-Saharan Africa, according to the UN Human Settlements Program (2022). It is also ranked third in West Africa in the tech startups index. Ibadan joined the UNESCO Global Network of Learning Cities in 2016.