In the Province of Leon, at Sahagn (or San Facondo), St. John was born in the year 1419. Juan González del Castrillo and Sancha Martnez were his parents, and they were wealthy family in the city. After sixteen years of infertility and frustration, he was their first child.

The Benedictines in his hometown provided him with his initial education. As was customary at the time, his father secured for him the benefice of the nearby parish of Dornillos, but John had serious moral concerns about this. He later met Bishop of Burgos Alfonso de Cartagena, who took a liking to the bright, exuberant young man and had him schooled at his home. He also awarded him many prebends, ordained him a priest in 1445, and appointed him a canon at the cathedral.

John resigned from all of his positions and kept only the chaplaincy of St. Agatha, where he devoted his time and energy to working for the redemption of souls, out of a conscious respect for the rules of the Church. He subsequently began to live a life of austere poverty and mortification.

He was permitted to enroll in the University of Salamanca after deciding that a deeper understanding of theology would be helpful. He completed a four-year course there and earned a degree in divinity. He served as the sacred minister for nine years at the College of St. Bartholomew's Chapel (St. Sebastian Parish) during this time.

He was subsequently forced to have surgery for stone removal, and while he was ill, he pledged that if he survived, he would become a religious person. Following his recuperation in 1463, he applied for admission for membership in the Order of Hermits of St. Augustine at Salamanca's St. Peter's Church, and on August 28, 1464, he made his profession. He made such strides towards spiritual perfection that he was soon named Master of Novices and elected Prior of the community of Salamanca in 1471.

St. John had such a deep love of the Blessed Sacrament that he frequently saw the Sacred Host radiant with splendor at Mass. It was difficult to trick him because of his unusual ability to see into the depths of the soul, and sinners were nearly always compelled to make sincere confessions.

As frequently as he could, St. John would spend hours in adoration of the Blessed Sacrament. St. John frequently experienced ecstasy while celebrating Mass, absorbing the majesty of Jesus, and conversing with Him.

John scourged the crimes and vices of the day, which the wealthy and aristocrats were outraged by while preaching the Word of God. His opponents quickly grew, even going so far as to hire assassins, but when they saw the calm and heavenly sweetness of his visage, they lost heart. Angered by the saint's harsh preaching against excess in dressing, some women of Salamanca publicly abused him in the streets and pelted him with stones until they were stopped by a guard patrol.

John's harsh words on the "sins of impurity" had a beneficial effect on a certain nobleman who had been living in open concubinage, but the women vowed vengeance. It was widely believed that she poisoned the saint, although this claim is only made in later biographies. He faced fierce criticism from some local officials as a result of his sermons against unclean living conditions and in favor of the rights and dignity of workers. He earned a reputation as a distinguished preacher, drawing sizable crowds and offering several chances for conversion with his honesty, and integrity.

On June 11, 1479, John passed away in his monastery. His remains were interred in the city's Old Cathedral. Following the start of the beatification procedure in 1525 under Pope Clement VII, he was proclaimed "Blessed" by Pope Clement VIII in 1601 and canonized on October 16, 1690, by Pope Alexander VIII. On June 12, Benedict XIII set his feast day.

The remains are currently housed on the main altar of the Salamanca Cathedral after being moved there on September 1st, 1835. His relics can be found in Spain, Belgium, and Peru. In works of art, he is shown holding a chalice and a host while being encircled by light. He is the patron saint of the city and diocese of Salamanca, Spain.

Other Saints of the Day
Saint Amphion
Saint Cuniald & Geslar
Saint Olympius
Saint Peter of Mount Athos
Saint Ternan