Ilagan, officially the City of Ilagan, is a 1st class component city and capital of the province of Isabela, Philippines. According to the 2020 census, it has a population of 158,218 people making it the most populous city in the province and the second most-populous in Cagayan Valley after Tuguegarao. As of 2022, it also had the most number of voters in the province with 101,050 electorates.