According to E. Rossoni, Bagliani is a surname of Piedmontese origin, particularly associated with the area of Alessandria. He proposes two main explanations for its origin: it may derive from the place name Casalbagliano, near Alessandria, or from the medieval personal name Balianus or Baliani, documented in the second half of the 12th century. This evidence suggests that the surname may have originated either as a habitational surname or as a patronymic derived from an ancestor's given name.

Rossoni places Bagliani within a broader group of related surnames, including Bagliano, Baglio, Baglione, and Baglioni, which share a common root and developed through regional linguistic variations.

Local historical traditions from the Alessandria area preserve a legendary account linking the Bagliani family to the Crusades. According to this tradition, an ancestor named Bagliano remained in Palestine and married Maria, the widow of King Amalric of Jerusalem. Their descendants were said to have founded Casalbagliano, documented as Baianus in 1192. While this narrative cannot be fully verified, it reflects the long-standing historical association between the surname and the Alessandria region.

Some scholars have also suggested that the name may ultimately derive from Ballianus, possibly connected to the ancient Roman family name Ballius, reinforcing the surname’s deep historical roots.

Overall, Bagliani is primarily regarded as a surname of Piedmontese origin, linked either to the locality of Casalbagliano or to the medieval personal name Balianus, with a long history in the Alessandria area and traditions reaching back to the medieval period.