On June 22, 1963, Republic Act (RA) No. 3728 was promulgated creating the municipality of Santa Teresita formerly known as Barrio Namunit. It was formally inaugurated as a municipality on August 27, 1963. It is composed of initial nine (9) barangays namely Alucao, Buyun, Dungeg, Luga, Masi, Mission, Namunit, Villa, and Tuyo. Barrio Namunit was the seat of local government being the most strategic and progressive location. This was later created into two (2) barrios namely Centro East and Centro West. Barangay Mission which is one among the barrios of Santa Teresita is believed to be a place historical with importance being the landing site of the Spanish Missionaries led by Juan de Salcedo of Spain in the year 1557. The mouth of the Mission River where they entered was believed to be the convergence area with the Rio Grande de Cagayan (Cagayan River) to the sea at that time.
Sta. Teresita is a 4th class municipality with 4 urban barangays and 9 rural barangays. Primarily an agricultural town with rice and corn as the major products. For tourism potential, the municipality is capable to offer natural attraction (caves & falls), cultural and historical heritage site and the bakong industry.
The state of economy and development of Sta. Teresita is continuously gaining its momentum by continuously exceeding its gross collections with an average growth rate of 14.15%.
The municipality of Santa Teresita, a 4th Income Class Municipality has been receiving various recognitions and awards given by the national, regional, and provincial award-giving bodies. Few to mention are the following: