The authors differ on the origin of this surname. E. Rossoni proposes derivations from anthroponyms: the name Staneus, of Greek origin though documented also in Roman times; the medieval Germanic name Stannus; the Gothic Stannis; or else an apocopated form of the Slavic name Stanislaw. Rossoni records the variant Stagni in the zone between Modena, Bologna and Ferrara, with groups also in Genoa and in Trieste; while the variant Stagno appears in Sicily —especially in the Palermo area, but also in the Agrigento, Messina, Catania, Caltanissetta and Enna areas—, as well as in the Vibo Valentia area and in the Cagliari area.

F. De Laurentiis proposes instead toponymic or descriptive origins: the surname could derive from the place name Stagno, present in the provinces of Bologna, Livorno, Parma and Cremona; from the trade term stagnaio ("tinsmith"); from a reference to places with small expanses of shallow water where marsh plants surface; or from a nickname applied to a solid, well-planted person.