The bay at Gamleby was at the centre of Tjust during late Iron Age. In other parts of the region, there were single farms. The in-lands of Tjust were more or less uninhabited. During the early Middle Ages, people moved to the wooded areas, and new land was cleared and farmed. Place-names with –ryd (cleared land), -hult (meadow) and –måla (claimed territory) indicate such settlements from the early Middle Ages.
The expansion in the early Middle Ages continued until the second half of the 14th century. In the summer and autumn of 1350, the plague (or Black Death) struck Västervik. Later that autumn it reached the remote parishes of Tjust. The effects of the plague were very severe, particularly so in areas with a small population. One effect of the plague was a decrease in farming during the latter part of the 14th and first part of the 15th century. Farming did not pick up until the end of the 15th century, because the plague struck time and time again; in 1363-66, in 1393-99, in 1404-06 and in 1411-16.
Many of the farmers in Tjust had their own property and paid taxes to the Crown. They were free-holders, "skattebönder". The farmers who farmed land owned by the gentry were tenant farmers – so-called "frälsebönder". They leased the farm from the nobleman and paid taxes to him. The lease would usually be renewed every six years. When the lease was up for renewal, an additional fee was often claimed. It might have been rather more troublesome to have been a tenant farmer than a free-holder.The church, the bishop and the convents were land-owners, too. Their tenant farmers were called church- bishop- or convent-farmers. They paid their taxes, or lease, to the church, the bishop or the convent.