San Giorgio probably sprang up as an outbuilding of the nearby Benedictine monastery, on the former locality of Monticello; San Giorgio, with its castle, soon grew into a major centre in the area. In 1250, it appeared on the list of estates under the dominion of Pavia and was subjected to the Beccaria family for a while. With the arrival of the Visconti and the Sforza families, it was subject of further infeudations.