Shomin refers to the people who belonged to shoen (manors) which were differentiated from the people who lived within koryo (public lands). Although shomin generally referred to hyakusho-myoshu (the cultivators/owners of rice fields) or zaike-jumin (lay believers/practioners of Buddhism), in the later generations, the term also included the cultivators of isshikiden (partially exempt fields) or sanden (deteriorated rice fields) as well as shoju (retainers) and genin (servants who served their masters as slaves).
In shoen of the earlier period, there were not people who were categorized as shomin, except slaves who directly belonged to the shoen owners or vagabonds who drifted from other provinces. The cultivators of shoen at that time usually lived in koryo outside shoen, and as for those who had dwellings within shoen, they had registered addresses in koryo. They were yoriudo (a dependent, frequently one who served a noble house or proprietor) who cultivated the fields of shoen (寄作), and had little involvement with the shoen itself. In order to ensure the stable number of cultivators, the shoen owners encouraged vagabonds to stay within shoen by providing them with seeds and everyday commodities.
During the process of the development of the shoen system and the demise of Kochi-komin sei (the system of complete state ownership of land and citizens), the shoen owners, by utilizing their political influence, endeavored to secure the cultivators as residents of their own shoen by entitling them to the exemptions of the public duties or the temporary odd-job duties; such a process is known as the establishment of myo taisei (local tax management system based on rice land). By the twelfth century when the shoen koryo sei (The System of Public Lands and Private Estates) came into force, the rule, in which the residents of koryo were regarded as komin and the residents of shoen were regarded as shomin, regardless of whether the cultivator works in the fields that belong to koryo or shoen, was established; and further, the rule in which the Kokushi (an officer of local government) can impose the fueki (corvee) of the province on komin, but not on shomin, was founded on January 21, 1130, according to Myobo-ke kanmon (Report by Judicial Officials). It was also around this time that the term 'shomin' appeared. Shoen at that time had a dual class structure, which was divided into the group which included the hyakusho-myoshu who owned myoden (rice field lots in charge of a nominal holder) and the zaike-jumin; and the group which included sakunin (tenant cultivators), kobyakusho (peasants who owned little plowlands), shoju, and genin. The former group belonged to the upper class which was in charge of the smooth operation of cultivation in shoen by recruiting sakunin and kobyakusho, and some of the influential figures in the group also became a shokan as a part of the managerial side of shoen. Shomin' in its original sense then referred only to the upper-class inhabitants. Those who belonged to the latter group, such as sakunin and kobyakusho, on the other hand, were given much less rights and security over the land they worked in comparison to hyakusho-myoshu and zaike-junin, as they were usually given a one-year contract and never had a possibility to attain a managerial post, in exchange for the partial payment of nengu for fields such as isshikiden and sanden. As for shoju and genin, they served and belonged to the upper-class members such as the shoen owner and shokan. There were also people without roots, such as hinin (outcasts) and kojiki (beggars), who belonged to the lowest of the class hierarchy and were discriminated against. However, during the fourteenth century, many factors, such as the improvement of productivity, the resistance of the class of peasants, and the downfall of the upper-class together with the advancement of the lower-class, contributed to the demise of the shoen-koryo sei. Further, there were those of the upper-class who attained the position as a landlord or a jizamurai (local samurai) which enabled them to break away from the rule of the manor owners and to establish their own business managing and renting their lands to local peasants. However, during the fourteenth century, many factors, such as the improvement of the productivity, the resistance of the class of peasants, and the downfall of the upper-class together with the advancement of the lower-class, contributed to the eventual demise of the shoen-koryo sei. Further, there were those of the upper-class who attained the position as a landlord or a jizamurai (local samurai) which enabled them to break away from the rule of the manor owners and to establish their own business managing and renting their lands to local peasants. On the other hand, the people who belonged to the lower-class fell to the even lower status of jigebyakusho, and there began, involving even the class of shoju and genin, the process of the reorganization of the class structure in the shomin populace.
As a result, the class of shomin, including shoju and genin, started to form groups of peasants which confronted the manor owners and the external parties, which was a process that eventually led to the formation of the self-governing organization called 'soson.'
At this stage, the term 'shomin' was no longer used as it gradually and naturally disappeared.