Irosin frequently experienced erosion due to river inundations. On December 24, 1933, massive flooding caused numerous fatalities. To prevent the violent surge of the river from eroding the town's mainland, a concrete river control dike was constructed in 1937 under Mayor Felipe Santiago and Congressman Norberto Roque.
Contemporary period On April 10, 1989, Irosin was defended by military and police forces, led by Lieutenant Antonio Dy, against approximately 200 communist rebels of the
New People's Army, which resulted in 20 rebel casualties; along with the deaths of three female civilians in the crossfire. Dy later received the "Medalya ng Kagitingan" Award in August for leading his 13 policemen to defend Irosin's municipal hall. The local tourism industry has significant potential, as ecological tourism is a global trend and the national government aims to develop Bicol as a major tourist hub. Given its variety of natural tourist spots and strategic location, Irosin serves as a convergence area for both foreign and domestic tourists and visitors. {{Weather box
Political geography Irosin is the only
landlocked municipality in Sorsogon province. Irosin is politically subdivided into 28
barangays, each consisting of
puroks, and some with
sitios. • Bagsangan • Bacolod (
Poblacion) • Batang • Bolos • Buenavista • Bulawan • Carriedo • Casini • Cawayan • Cogon • Gabao • Gulang-Gulang • Gumapia • Santo Domingo (Lamboon) • Liang • Macawayan • Mapaso • Monbon • Patag • Salvacion • San Agustin (
Poblacion) • San Isidro (Palogtok) • San Juan (
Poblacion) • San Julian (
Poblacion) • San Pedro (
Poblacion) • Tabon-Tabon • Tinampo • Tongdol ==Demographics==