Tagnocon derived its name from a very tiny creature called “TAGNOC” found in a very small creek situated in the land occupied by Pedro Marfe, now a part of the barangay. By virtue of a resolution promulgated by barangay Mainit and approved by the Provincial Board on May 14, 1969. Tagnocon became a barangay and was inaugurated on June 29, 1969.
There are 8 creeks/rivers that drain the barangay: Batinag Creek; Pagdagaan Creek; Casimsiman Creek; Cabao Creek; Piagbangatan Creek; Inopuan Creek; Manat River and Bugac Creek.
In Tagnocon, there is a total area of 1,920 hectares and 1,294.58 hectares of which is planted to crops, such as: coconut (1,096.58 has.), coffee (50.6 has.), corn (50.6 has.), Lanzones (32 has.), banana (20 has.), durian (20 has.), rootcrops (20 has.) and other crops. Considered major crops of the barangay are: coconut, corn, coffee and varied fruits