According to folk legend, the name Casiguran was obtained from the Ilocano term Sigod which means "edge" or "maximum", which is due to the location of the Municipality at the northern edge of Aurora Province. (Another translation & definition of sigod is "soon" or "early") Another legend says that if an unmarried stranger comes to the place, he unavoidably falls in love and marries and most of the time stays for good. The affixation of sigod when converting it to a noun is kasigudan, from which the Hispanized pronunciation "Casiguran" is derived.
In 1902, Casiguran became part of the province of Tayabas (now Quezon).[8] In 1905, the area of modern Dilasag was part of Nueva Vizcaya & transferred to Tayabas thru Casiguran.[9] From 1906 to 1907, Casiguran was merged with the town of Baler, also then in Tayabas.[10][11] Casiguran was transferred to Nueva Vizcaya in 1918, but restored to Tayabas in 1946.[9][12]
In 1942, invading Japanese forces landed in the town of Casiguran.[further explanation needed] On February 19, 1945 to May 11, 1945, Allied troops as well as Philippine Commonwealth forces and recognized guerrilla units fought on the Battle of Casiguran during the return of American forces on Luzon on World War II.[further explanation needed] When the Philippines regained sovereignty in 1946, Aurora was still part of Tayabas and Casiguran was a lone northern town. Its political jurisdiction is bounded on the north by the province of Isabela, on the west by Quirino, and on the south west by Barangay Dinadiawan, which was then the boundary between Baler and Casiguran.
In 1959 and 1966, the barrios of Dilasag and Dinalungan, which were part of Casiguran and situated on its northern and south-western portions, were made into municipalities.[13]
According to the Philippine Statistics Authority, the municipality has a land area of 715.43 square kilometers (276.23 sq mi)[14] constituting 22.73% of the 3,147.32-square-kilometer- (1,215.19 sq mi) total area of Aurora.
Casiguran is located 120 kilometers (75 mi) north-east of provincial capital Baler and 351 kilometers (218 mi) from Manila. It is bounded on the north-east by Dilasag, south-west by Dinalungan, north-west by Quirino and southeast by the Philippine Sea.
Barangays
Casiguran is politically subdivided into 24 barangays.[15] Each barangay consists of puroks and some have sitios.
In the 2020 census, Casiguran had a population of 26,564.[3] The population density was 37 inhabitants per square kilometre (96/sq mi).
In 1960, the population of Casiguran was 6,900. This was almost doubled by the 1970s when population was 12,128, an increase of about 76% (5.8% annual average growth rate). Between 1970 and 1975, there was a marked decreased in the number of population from 12,128 to 11,670. This reduction was due to deteriorated peace and order, which forced some of the population to move away. The trend reversed by 1980, with an increase of 19% or an annual average growth rate increase of 3.86%. Increasing population continued during the succeeding censal years (1980 to 1995) but with a declining annual average population growth rate. This is attributed to the gradual stoppage of logging operations in the area. Many workers involved in this trade were not original residents, so when the jobs were no longer available, they left. Between 1995 and 1999 there was a significant increase of the annual average population growth rate to 4.36%.