The settlement now known as Sto. Tomas was once called Baliwag, because many of its early Catholic parishioners were always late in attending Mass and other religious activities. Of course, this character trait was not only true of the early Thomasians but of early Filipinos in general.

The Municipality of Minalin was the original mother town of Baliwag on September 15, 1792 upon the approval of Governor General Felix Berenguer y Mariquina. Baliwag was later renamed in honor of Saint Thomas the Apostle. Parish records of baptisms, marriages and deaths from January 1, 1830 1854 have the towns name written as Santo Tomas de Baliwag.
Then from 1855 to 1926, its recorded name was Pueblo de Santo Tomas.

When the town was reconstituted in 1903 under the administration of American Governor General Robert William Howard Taft, the town of Minalin was unespectedly annexed to Sto. Tomas and placed under its political jurisdiction for a brief period until July 25, 1904. The Honorable Gregorio Pineda was appointed as Municipal President during that brief union of the two towns.
On January 2, 1905, for economy and administrative efficiency, Sto. Tomas and Minalin where both consolidated with the Municipality of San Fernando. Don Francisco Hizon was then the mayor of San Fernando, while Don Macario Arnedo of Apalit was the provincial governor of Pampanga.

Sto. Tomas was inaugurated again as an independent municipality on January 11, 1952 after a long campaign led by Patricio Gomez, a municipal councilor of San Fernando, to separate the six barrios of Sto. Tomas, San Matias, San Vicente, San Bartolome, Sto. Rosario and Poblacion from political jurisdiction of the provincial capital. The Honorable Patricio Gomez was initially appointed by President Elpidio Quirino as the first mayor of the newly recreated municipality with the seat of the municipal government temporarily located in his house in barrio San Matias.

In 1955, Republic Act 1250 was enacted by the Philippine Congress and approved by President Ramon Magsaysay transferring the Sto. Tomas seat of municipal government to barrio Poblacion. However, on June 11, 1978, President Ferdinand E. Marcos issued Presidential Decree No. 1441 which permanently transferred the seat of municipal government to barrio San Vicente. The new location of the municipal hall is said to be more strategic for the purpose of accelerating economic development in Sto. Tomas.
Although the population of Sto. Tomas has been consistently increasing from 21,382 in 1975 to 38,483 in 2000, as per the National Census compiled by the Provincial Planning Office – its geographical area remains the same 21.29 square kilometers. Economic growth and increases in population initiated the creation of two barangays in 1970. These two barangays, Sapa-Santo Niño and Moras de la Paz, were former sitios of the progressive barrio of San Matias. The

Catholic parish church of San Matias is currently undergoing a major renovation, coordinated by Father Marlon Vitug Cunanan.

*Rudy Ordoñez (2009). The Kapampangan Mystique