"Jokoku" (second-biggest provinces next to Taikoku) is one of grade classifications of provinces governed in accordance with the Ritsuryo codes.
It was almost established in the period when the ritsuryo system, which was centralized governing system, was put in place. The Imperial Court decided local administration sections in order to establish centralized administrative framework and divided various provinces into four grades in accordance with political power, economic power and national power such as land area, kokudaka (crop yield), population.
Taikoku (ryoseikoku) (major provinces)
Jokoku (second-biggest provinces next to Taikoku)
Chugoku (ryoseikoku) (middle-sized provinces)
Gekoku (minor provinces)
Jokoku was a second-biggest province. However, the standard of grade classifications was not clear. In addition, grades of official court rank for Kokushi (provincial governor) were differentiated in accordance with the grade of provinces.
Also, provinces were classified into ongoku (far countries), chugoku (middle countries), kingoku (near countries) in accordance with the distance from Kyoto.