San Isidro, officially the Municipality of San Isidro, is a municipality in the province of Nueva Ecija, Philippines. According to the 2020 census, it has a population of 54,372 people. San Isidro, along with its origin Gapan, Aliaga, Cabiao, and San Antonio were parts of Pampanga until they were transferred to Nueva Ecija in 1848. It served as the capital of Nueva Ecija from 1852 to 1912. After the first cry against the Spanish colonial government was made in 1896, there were 2,000 revolutionary soldiers under General Mariano Llanera who sieged San Isidro.