Excavations of the remains of the medieval church of Santa Maria di Campogrosso (Sicily) were conducted by the Institute of Archaeology and Ethnology of the Polish Academy of Sciences as part of scientific cooperation with Soprintendenza per i Beni Culturali ed Ambientali di Palermo. Based on the records of post-medieval historians, the construction of the church was placed in the second half of the 11th century, which contradicts the findings of architectural historians, who dated the building to the 13th-century and even later. As a result of archaeological excavations carried out in 2015–2018, it was possible to locate unknown fragments of the church’s structure and the remains of the cemetery adjacent to it. The 14C dating carried out for samples obtained from the walls of the existing building as well as from bone remains from the churchyard in combination with stratigraphic information from archaeological trenches and the chronology of coins indicates a high probability of the church construction in the second half of the 12th century and confirms the end of the monastery complex existence at the end of the 13th century.