Saint Jerome Hermosilla was born on December 30, 1800 in Spain into a poor but virtuous family. He studied at the seminary run by the Dominican Order. At age 19, Jerome made his solemn profession in the Dominican Order at the Convent of St. Dominic in Valenza on October 29, 1823 and was ordained a deacon.
He volunteered for missionary work in the Far East. On March 2, 1825, he and 11 other Dominican friars set sail for Manila, Philippines. In 1826, he was ordained a priest and became the Director of the Rosary Confraternity in Manila.
On October 23, 1828, he was sent by his superiors to evangelize in Vietnam. On May 15, 1829, he arrived in Thai Binh, which belonged to the Vicariate Apostolic of Eastern Tonkin.
During 1830-1832, King Minh Mang severely persecuted Catholics. In the vast vicariate with many faithful, only 3 elderly and weak priests remained. Bishops Delgado and Henares gave Hermosilla the Vietnamese name Vong, as he represented the young generation succeeding the elders. On March 25, 1841, he was appointed bishop to succeed the two deceased bishops. The situation was relatively calm during the 7 years under King Thieu Tri's reign.
During this time, Bishop Hermosilla-Vong devoted himself to restoring destroyed churches and chapels, opening catechism schools, acquiring liturgical items, etc. His top priorities were conferring sacraments to the faithful, seeking out those who had left the faith, and promoting the Rosary devotion. He also re-established seminaries, convents, gathered dispersed nuns, and ordained 7 new priests.
Under King Tu Duc, persecution intensified. Bishop Hermosilla-Vong had to use the aliases Liem or Tuan to evade capture. On October 21, 1861, while hiding with the catechist Nguyen Duy Khang in a non-Catholic home, they were discovered. They were arrested and taken to Hai Duong.
Before the mandarin authorities, Bishop Hermosilla-Vong declared: "The Catholic faith is the true religion, teaching mankind to honor God and love one another, so that after death they may enjoy eternal bliss in Heaven, it is not a false sect. To die for this faith is my great happiness." He was sentenced to death by beheading on November 1, 1861 at the Nam Mau execution grounds outside Hai Duong.
His remains were buried by a non-Catholic sympathizer named Oanh in Tho Ninh village, later transferred to the chapel of the Amantes Crucis Congregation in Ke Mot for veneration.
Bishop Hermosilla-Vong was beatified on May 20, 1906 and canonized on June 19, 1988.