The artefacts, which Sisto collected over the years, were stolen from town archives, libraries and churches in the southern regions of Puglia, Sicily and Molise, and exported illegally, Italian police said.
After Sisto's death, his two sons contacted U.S. authorities after discovering the collection scattered around the family home in Berwyn, Illinois.
The trove included 348 parchments dating back as far as the 12th century, more than 400 archaeological artefacts, and documents signed by famous Italians including 19th century unification hero Giuseppe Garibaldi.
"We are returning to Puglia artefacts taken by an immigrant who wanted too many reminders of his own land," said Colonel Luigi Cortellessa, deputy head of the police department in charge of protecting Italy's cultural heritage.
It was not clear how Sisto got hold of the artefacts. Police said Sisto's sons were unaware of their father's activities and contacted US authorities because they did not know what to do with the antiquities.
Italy, together with archaeological powerhouse Greece, has stepped up international efforts in recent years to return looted antiquities smuggled to foreign museums and private collections.
Italy dropped a high-profile lawsuit against California's Getty Museum in 2007 when it agreed to return 40 items and signed a loans and co-operation agreement.
