In 1860, its 723 inhabitants unanimously agreed to join the Kingdom of Italy. During World War II, partisans from the Siena zone started their first organizational operations in Monticiano, where a resistance brigade, named after Spartaco Lavagnini, also operated. The night time battle between the partisans and the Germans between the 3rd and 4 June 1944 which took place in the town's central piazza is particularly remembered.