Province of Genoa
The Diocese of Tortona () is a Roman Catholic ecclesiastical territory in northern Italy, spanning parts of three regions of Piedmont (Province of Alessandria), Lombardy (Province of Pavia) and Liguria (Province of Genoa). It is a suffragan of the Archdiocese of Genoa and forms part of the ecclesiastical region of Liguria. The diocese claims to be one of the oldest in Lombardy and the Piedmont.