Long before it became a town in the year 1801, Sipocot originally belonged to the town of Lupi , being one of its barrios. Its conversion into a town also paved the way for the establishment of its parish in dedication of St. John the Baptist, the town's patron saint. This marked the beginning of the celebration of the town fiesta held annually every June 24.

A version known to the local residents concerning the roots of the name of the municipality tells about the coming of the Spaniards to the Philippines, where a certain Captain Aguire of Lupi spent his leisure hours fishing in the cool water of Vigaan River in the morning and in the afternoon he would sail back by banca in the Bicol River. He usually have a plentiful catch which would be more his family needs. This activity did not escape the Spanish encomienderos’ ears in the town of lupi and the said Captain was summoned by the Spaniards for questioning. However, in the process of the inquiry, the Captain misunderstood and misinformed the foreigners and pointed to the Bicol River as his fishing area.
 
Source:
Wikipedia.org