During the Spanish Era, the municipality was only a component "barrio" of Gapan. When San Isidro became a town and was separated from Gapan, the town and San Antonio became one of its component barrios. When San Antonio itself became a town, the area was still its component "barrio" called San Agustin. By 1865, Jaen was known by its old name "Ibayong Ilog", and because there were many people in the river port in what is now Barangay Langla, the town became a centre for trade.