John of Sahagún, (24 June 1419 – 11 June 1479) was a Spanish Augustinian friar and priest. He was a leading preacher regarding social behavior of his day. He was declared a saint by the Catholic Church in 1690 by pope Alexander VIII.
John was born in the year 1419, at Sahagún (or San Facondo) in the Province of Leon. He was the oldest of the seven children of Juan González del Castrillo and Sancha Martínez, a wealthy family of the city.
González received his early education from the monks of the Royal Monastery of St. Benedict in his native city, a leading religious and educational center in the region known as the Cluny of Spain. He received the tonsure while still a youth, according to the custom of the times, after which his father procured for him the benefice of the neighboring parish of Tornillo. He was later introduced to Alfonso de Cartagena, the Bishop of Burgos (1435–1456), who was impressed by the bright, high-spirited boy. Cartagena had him educated at his own residence, gave him several prebends, ordained him a priest in the year 1445, and made him a canon at the Cathedral of Burgos.