Chigyo-koku indicates the provincial system and province in ancient and medieval Japan in which dominant nobles, shrines or temples acquired chigyo-ken (also called Kokumu-ken or rimu) (the right to manage the province) and obtained their revenues from there. A dominant noble, shrine or temple that acquired chigyo-ken was called chigyo-kokushu (provincial proprietor), and chigyo-kokushu had the right to make a recommendation of kokushi (provincial governors) of the province and the right to get kanmotsu (tribute goods paid as taxes or tithes). Chigyo-koku was also called "sata-koku" or "kyu-koku" as well.
Chigyo-koku originated in the Ingu bunkoku-sei system (see the following description) in the middle era of the Heian period. The ingu bunkoku-sei system is the system in which Innomiya families (the families of Daijo Tenno (the Retired Emperor), nyoin (a close female relative of the Emperor or a woman of comparable standing), Empress, chugu (the second consort of an emperor) and Togu (the Crown Prince)) were given the right to make a recommendation of kokushu (or zuryo (the head of the provincial governors)) of a specific province and were also allowed to get the kanmotsu dedicated by the province. The ingu bunkoku-sei system existed from the early 10th century. It was customary that Innomiya families appointed their close retainers or relatives to kokushu and zuryo.
In the era from the 11th century to the 12th century, powerful nobles introduced a system similar to the ingu bunkoku-sei system as well. With their political power as a background, it gradually became a custom that powerful nobles appointed their relatives or dependents to zuryo of specific provinces, and they acquired, as their revenues, the salary and tax gained by the zuryo they sent to the provinces. This was the origin of the chigo-koku system.
The ingu bunkoku-sei system and the chigo-koku system were different originally. The ingu bunkoku-sei system was an official system of the nation, and Innomiya families were allowed to acquire, as their revenues, the kanmotsu dedicated by the ingu bunkoku provinces. On the other hand, the chigo-koku system was not approved officially. Therefore, the kanmotsu dedicated by the chigyo-koku provinces had to be delivered to the nation, with only the salary and tax gained by the zuryo (which originally should be zuryo's won income) allowed to be acquired by chigyo-kokushu. Therefore, it could occur that a province was not only a bunkoku (a province under control) of an Innomiya family but also a chigyo-koku province under control of a noble, shrine or temple, and it is considered that such examples existed actually. In this case, the kanmotsu dedicated to the nation was delivered to the Innomiya family concerned and the salary and tax gained by the zuryo was paid to the chigyo-kokushu.
Ingu bunkoku provinces and chigyo-koku provinces increased rapidly in the insei period (during the period of the government by the Retired Emperor) (in the latter half the 11th century and later). It was not rare that Sessho (a regent) or Kanpaku (the top adviser to Emperor) had two or three chigyo-koku provinces. Initially, the chigyo-koku system was used mostly by powerful nobles. However, from the latter half of the 12th century, the chigyo-koku provinces controlled by shrines or temples and those by samurai appeared. It is said that, in the Taira clan government towards the end of the Heian period, thirty plus provinces became chigyo-koku provinces of the Taira clan. When the Kamakura bakufu (Japanese feudal government headed by a shogun) was established towards the end of the 12th century, nine provinces in the Kanto region became chigyo-koku provinces of Kamakura-dono (lord of Kamakura), or provincial territories belonged to the Kamakura bakufu. Suo province that was assigned to the task of reconstructing Daibutsu-den Hall (the great Buddha hall) of Todai-ji Temple was virtually a chigyo-koku province of Todai-ji Temple, and the province continued being under control of Todai-ji Temple even after the work to reconstruct Daibutsu-den Hall was completed. In this way, the number of chigyo-koku provinces continued increasing, and it is recorded that 50 chigyo-koku provinces existed in 1215.
In the Kamakura period, the chigyo-koku system became officially recognized gradually. At the same time, chigyo-kokushu came to mean handing over their chigyo-koku provinces to their heirs, and fixing the relationship of chigyo-kokushu with specific provinces. The provincial territories belonging to the Kamakura bakufu and Suo, a chigyo-koku province of Todai-ji Temple were typical examples. In addition, Tosa Province and Iyo Province were also other chigyo-koku provinces of the Ichijo family and that of the Saionji family, respectively. The right to acquire kanmotsu was given only to Innomiya families. However, as the chigyo-koku system became recognized officially, some of the chigyo-kokushu were bestowed the right to acquire kanmotsu.
Entering the Muromachi period, the right of Shugo (provincial constable) was expanded actively. As a result, the Shugo who acquired the following rights came to control the province territorially: the right to control Karita-rozeki (to reap rice illegally), the right to send a delegate for executing the bakufu's order, the right to collect half of the taxes from manors and demesnes as military fund, the right to confiscate land property from criminals or if it is left derelict, and the right to collect temporary special tax levied on arable land. When kokuga (provincial government offices), which was the core site of controlling a chigyo-koku province, became placed under control of the Shugo in such a process, the chigyo-koku province became extinct.