Mendrisio is first mentioned in 793 as Mendrici.
Some thirty graves, tombs and grave stones, as well as coins from the Roman Republic and Roman Empire and the remains of a villa near the Church of S. Maria indicate that this area was settled throughout the Roman era. Powerful Langobard families made Mendrisio into a regional power, at the expense of the old power center, Balerna. By 1140 Mendrisio was an independent municipality in the county of Seprio. It was ruled by city of Como from 1170 until 1335. Following the victory of Milan over Como, it was ruled by the Milanese Visconti. The Visconti ruled until 1402, when a victory by Como brought Mendrisio back under that city. In the 15th Century, it became a fief held by the Rusca and Sanseverino families.
During the Middle Ages a number of secular buildings, including several massive towers, were built in the town between the Porta San Giovanni and the river Moree. On the hill on the other side of the river, the Torriani family built a castle, which was destroyed in the Late Middle Ages. Under the Swiss Confederation's rule, it became the capital of the bailiwick of Mendrisio. Starting in the 17th Century, the governor of the bailiwick took up residence in the Palazzo Rusca.
The population of the town divided into three separate groups, the nobles or nobili, the burghers or borshesi and the newcomers or divisi. The divisi was a class of residents that did not have full citizenship rights in the town. They were made up of tenants, new residents and their decedents. While the divisi had rights and access to the commons, their rights were restricted. The population of Mendrisio remained divided into three classed until the end of the old village cooperative (vicinia) in 1798.
Well before 1000, the Church of Mendrisio formed a nearly independent church district, under the mother church of Balerna. In the 15th Century, it broke away completely from Balerna. In the town itself there were the
