Ilagan, officially the City of Ilagan (Siudad nat Ilagan; Iloko: Siudad ti Ilagan; Filipino: Lungsod ng 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. As of 2022, it holds the title as the most number of voters in the province with 101,050 electorates.