San Giacomo lies in a hilly landscape a few miles from the Adriatic coast, and is a quiet, farming village a little distance from Termoli, which is the biggest center in the vicinity.
In the area called San Pietro there are remains of a Roman villa of the Republican period (before the 1st century BC, then the next historical information record San Giacomo as a fiefdom of the Bishopry of Termoli from 1000 to 1806. The bishops had a number of farms (called "casali") in the area where the town rises today. One of these casali, situated on the hill called today Contrada delle Piane, belonged to the Templar Knights, probably as a checking point and resting refuge for the pilgrims traveling to the southern ports of Apulia, on their way to the Holy land.
In the late 14th century San Giacomo was under the jurisdiction of Termoli. The place was hit by the ruinous earthquake of 1456, which killed thousands of people in southern Italy. Local historians mention an almost complete destruction of San Giacomo (that was the name at the time). In the following decades the few survivors were joined by Croatian immigrants, brought to work on the farms and concentrated around the church, where the present town afterwards was built. These immigrants were called "Schiavoni" and this gave the place its name since 1564.