Ilagan, officially the City of Ilagan (; ) (PSGC: 023114000], is a component city in the province of Isabela, Philippines. It is the provincial capital, the most populous city in the province, and with a total land area of , the largest city in the island of Luzon and the fourth largest city (in terms of land area) in the Philippines, after Davao City, Puerto Princesa and Zamboanga City. Ilagan City has a population of 135,174 according to 2010 census.