Ilagan Day, observed in the city of Ilagan, Isabela, Philippines, takes place every May 4 to commemorate the city's founding anniversary. This special non-working holiday celebrates Ilagan's rich cultural heritage and local pride through various festive events, including cultural performances, pageants, parades, and sports competitions. The city, which is the most populous in Isabela and the largest by land area on Luzon, has a historical background that dates back to its founding as a town on May 4, 1686. The name "Ilagan" is believed to derive from the Ibanag word "nagali," meaning "transfer," reflecting the town's relocation for economic and security reasons. Ilagan Day was first designated as a holiday in September 2002, and it should not be confused with Ilagan City Charter Day, which is celebrated on August 11 to mark the city's official cityhood in 2012.