Iloilo (/ˌɪloʊˈiːloʊ/ ih-loh-EE-loh; [ɪlo.ˈilo]), officially the Province of Iloilo (Hiligaynon: Kapuoran sang Iloilo; Kinaray-a: Kapuoran kang Iloilo; Tagalog: Lalawigan ng Iloilo; Spanish: Provincia de Iloílo), is a province in the Philippines located in the Western Visayas region. Its capital and largest city is Iloilo City, the regional center of Western Visayas and politically independent from the province. Iloilo occupies the southeast portion of the Visayan island of Panay and is bordered by the province of Antique to the west, Capiz to the north, the Jintotolo Channel to the northeast, the Guimaras Strait to the east, and the Iloilo Strait and Panay Gulf to the southwest. Iloilo City is the center of the Iloilo–Guimaras metropolitan area or Metro Iloilo–Guimaras, and is geographically located in the province and grouped under it by the Philippine Statistics Authority, but remains politically independent from the provincial government. According to the 2024 census, the population of the province (excluding Iloilo City) is 2,082,616. If Iloilo City is included, the population is 2,556,344 in total.

Iloilo is known for its rich history and cultural heritage. The southern part of the province is home to many Spanish-era historic sites, including the Miag-ao Church, a UNESCO World Heritage Site in the Philippines. It also boasts several other prominent structures, such as the San Joaquin Campo Santo, San Joaquin Church, and Santa Barbara Church, all recognized as National Cultural Treasures by the National Museum of the Philippines. In the northern part, it is known for beaches and islands, including the Bantigue Sandbar, Tangke Lagoon, Cabugao Island, and Antonia Island, all part of the Islas de Gigantes. Additionally, Sicogon Island, situated south of the group of islands, has gained popularity as a luxury tourist destination.

The name of the province is derived from Iloilo City, which in turn is derived from the older name "Irong-irong" (archaic Hiligaynon writing: Irong̃-írong̃) meaning "nose-like", referring to the promontory between two rivers (Iloilo and Batiano) where the Fort San Pedro and the 17th-century Spanish port were located.

No pre-Hispanic written accounts of Iloilo and Panay island exist today. Oral tradition, in the form of recited epics like the Hinilawod, has survived to a small degree. A few recordings of these epic poems exist. The most notable are the works of noted Filipino Anthropologist Felipe Jocano.

While no current archaeological evidence exist describing pre-Hispanic Iloilo, an original work by Pedro Alcantara Monteclaro published in 1907 called Maragtas details the alleged accounts of the founding of the various pre-Hispanic polities on Panay Island. The book is based on oral and written accounts available to the author at the time. The author made no claim on the historical accuracy of the accounts.

According to Maragtas, Madja-as was founded after ten datus fled Borneo and landed on Panay Island. The book then goes on to detail their subsequent purchase of the coastal lands in which they settled from the native Ati people.

Datu Paiburong, one of the ten fleeing datus, established a settlement and named it Irong-Irong after an islet of the same name on the Batiano River. Afterwards, the warriors Labaodungon and Paybare, upon advice of datu Paiboring then recruited local fighters from the Philippines and fellow immigrants from Borneo and they returned to Borneo at Odtojan where the enemy of the ten datus, Makatunaw, ruled, Rajah or Sultan Makatunao, and they killed him and sacked the city he ruled and returned to the newly founded towns of the ten datus.

Spain eventually succeeded on conquering of the island of Panay when Spanish conquistador Miguel López de Legazpi moved his headquarters from the island of Cebu and creating the first Spanish settlement in the island in Ogtong in 1566. This is mainly due in part to the rivalries between the Bisaya and the Moro, of which the former found an ally in Spanish against the latter. The Bisayas accepted alliances with Spain, to defend themselves against the enslaving Moros. To this end, Iloilo contributed troops in the Castille War against the Sultanate of Brunei.