Ilagan, officially the City of Ilagan, is a component city and capital of the province of Isabela, Philippines. According to the 2024 census, it has a population of 164,020 people, making it the most populous city in the province and the second most-populous in Cagayan Valley after Tuguegarao. As of 2025, it also had the highest number of voters in the province, with 105,526 voters.