Pre-1500 — Ancient settlement#
Oyo-Yoruba settle the savannah margin north of the forest under the Alaafin lineage, claimed from Oranmiyan (son of Oduduwa, c. 12th–13th c.).
1500 — 1804 — Pre-colonial polities#
Old Oyo (Oyo Ile / Katunga) becomes a cavalry empire from the 16th century, tributary lord of Dahomey (Battle of Kana, 1698) and a major Atlantic slave-exporter via Porto Novo and Whydah. Alaafin Abiodun (r. 1770–89) marks its zenith. See Old Oyo Empire.
1804 — 1903 — The long 19th century#
Are-Ona-Kakanfo Afonja revolts c. 1817 against Alaafin Aole at Ilorin, allying with the Fulani Sheikh Alimi; the Sokoto jihad consumes Ilorin (1823). Old Oyo is sacked c. 1835; Atiba founds New Oyo at Ago-d'Oyo (Oyo-Atiba) c. 1837. The Yoruba Civil Wars (1820–93) see Ibadan emerge as the Oyo successor military power. The Battle of Osogbo (1840) halts Ilorin's southward expansion. Treaty of Kiriji (23 Sept 1886) with British mediation; final peace at the Treaty of 18 Feb 1893 at Lagos with Governor Carter.
1900 — 1960 — Colonial provinces#
Oyo Province within Southern Nigeria (1914), then Western Region. Ibadan becomes the capital of the Western Region (1939); the largest city in tropical Africa until the 1960s.
1960 — present — State creation chain#
- 1967 — Western State (capital Ibadan).
- 3 Feb 1976 — Murtala creates Oyo State (capital Ibadan).
- 27 Aug 1991 — Osun hived off.