Those who were firstly appointed to the kokushu of the above three provinces in 826 were Imperial Prince Kaya (Taishu of Hitachi Province), Imperial Prince Nakano (Taishu of Kazusa Province), and Imperial Prince Kadoi (Taishu of Kozuke Province) and all of them were Emperor Kanmu's princes.
天長3年に初めて3国の太守に任じられたのは、賀陽親王（常陸国太守）、仲野親王（上総国太守）、葛井親王（上野国太守）で、いずれも桓武天皇の皇子であった。