The Diocese of Bilbao includes the Historical Territory of Bizkaia, with the exception of the enclave of Orduña, which belongs to the Diocese of Vitoria. The municipality of Villaverde de Trucíos is also integrated into the Bilbao Diocese, although it belongs to the Community of Cantabria. Santander, Vitoria and San Sebastián are bordering Dioceses. It has an area of 2,193.17 Km2. It presently has a population of 1,139,012 inhabitants covered by 114 town councils.
The common name of the Diocese is Bilbao, capital city of Bizkaia, one of the historical territories belonging to Euskal Herria. The Latin name, nevertheless, is "Dioecesis Flaviobrigensis", imposed by the Bull for the erection of the Diocesis on 2nd November 1949. The historian A.E. de Mañaricúa thinks that this name supposes that Bilbao was the place where the "Flaviobrigensium Colony" was settled, something that he considers unlikely.