When the place improved and its population grew to no less than 5,000 people, it became a town through a petition filed by the inhabitants through the initiative of two early leaders, "Kabesang" Prudencio Esquivel and "Kapitan" Antonio Embuscado. On June 18, 1865, Jaen itself partitioned from San Antonio, and retained Saint Augustine of Hippo as its patron saint. The Spanish officials signed the papers granting the petition that "Ibayong Ilog" be a town in Factoria (now San Isidro) which was then the capital of Nueva Ecija. The declaration was brought to Governor-General Juan de Lara e Irigoyen in Manila, and afterwards was submitted to the Vice-General of the Philippines in the person of Rev Gregorio Martínez. Father Martínez marked the document as approved but later wrote in his own wish that the name "Ibayong Ilog" be changed to the name of his birthplace of Jaén, Spain.