On July 11, 1869 Pio Valenzuela was born in Polo, Bulacan to well to-do parents. His first schooling was in his home. In 1880 he learned Latin and Spanish from Telesforo Evangelista in Quingua. In 1884 he went to Colegio de San Juan de Letran where he finished his secondary course. In 1888, he enrolled at the University of Sto. Tomas.
When the Spanish colonial rule was becoming intolerable, he joined the Katipunan when he was just 22. He became the Surgeon General of the movement. Bonifacio and Valenzuel became close friends. They discussed many things about the Katipunan. He was instrumental in organizing many katipunan chapters especially in Bulacan.
When Rizal was in Dapitan, he was able to visit him to convince him to join the cause. He also offered Rizal the plan of shipping him to Hong Kong. Failing to convince Rizal, he sailed home and reported to Bonifacio.
Armed with a few bolos, guns and spears they attacked enemy camps and was able to relay the Cry of Balintawak to many Katipunan chapters in the neighboring towns. When the Spaniards discovered the movement, he was arrested and jailed at Bilibid prisons.
After the signing of the Treaty of Paris he was released.
He became Presidente Municipal of Polo in September 6, 1899 while still in prison. He became the District Health Officer in 1917. in 1921 he became governor of Bulacan. He was know for being upright and did not tolerate graft and corruption. He died April 6, 1956 leaving behind his wife Marciana and 7 children
On September 6, 1899, the Americans imposed military rule, and Dr. Po Valenzuela was named the town's first president. In February 1902, he resigned.
In 1904, Rufino Valenzuela was elected as the town's first president.
The Japanese made their way into Polo without encountering any opposition. Polo prospered during the Japanese occupation because it became a market town. There were greater signs of cooperation and social contact among the residents, but dread of retaliation from the Japanese ruled the day. The town was likewise turned into a terrifying environment. There were far too many homicides. The area became a haven for Makapilis and spies who caused havoc among the calm inhabitants.
On December 10, 1944, the reign of terror came to an end. For the inhabitants of Polo and Obando, it was a day of sadness because it was the day that the Japanese killed over a hundred males in both towns. Cries could be heard from the municipal building from approximately 1:00 a.m. till the sun set on this day, when males who had been screeded by the "Magic Eye" within the church were being tortured to death. (Perhaps this is why the old church was not rebuilt and was left to rot, prompting the construction of a new structure alongside the old.) Mayor Ponciano suffered the same fate. On this day, he died a horrible end with the city officials.
When the town was liberated, the advancing armed forces of Filipinos and Americans used flame throwers and shelled the town's large houses, including the more than 300-year-old church of San Diego.
The Japanese demolished the famous old bridge, dividing Polo into two pieces, the northern and southern parts. The northern section was immediately liberated by Filipino and American forces, while the southern part, which included the Poblacion, remained under Japanese control. When combined American and Filipino troops were able to cross the river and take the town on February 11, 1945, the Japanese surrendered.