The first mention of Zasmuky is from the year 1285 when it was a fortress of the Thane Sulislav of Zasmuk, kitchen master to Queen Guta, the wife of King Vaclav II. (1271 - 1305). The Thanes of Zasmuk owned the fortress until 1533 when it was bought by Adam from Rican, the district executive, who rebuilt the fort into a squared renaissance castle with open arcades into the courtyard. The former moat was made into vast stables, above them what may have once been a theater. It is now known as "The small Castle". The son of Adam, Zdislav from Rican, brought the estate into debt and in 1583 the chamber of justice sold Zasmuky to Jan Vchynsky/Kinsky, Burgrave of Karlstein.

The thirty year war greatly damaged these parts of the country. Villages were looted, some totally disappeared, 60% of the inhabitants vanished. The estate of Zasmuky was bought by a profiteer, Vaclav Michta, who, within a year (1637) exchanged it with Jan Rudolph Sternberg.

Adolph Vratislav from Sternberg (1630 - 1703), highest Burgrave of the Kingdom, inherited Zasmuky and rebuilt it in the spirit of the early Baroque by adding a tower, replacing the fortification with a park, creating a series of buildings for administration and farming trade and building a huge entrance tower into the complex, the portal decorated with his coat of arms, the eight pointed star. In 1690 Adolph Vratislav also bought the castle of Castolovice and turned Castolovice and Zasmuky into the Sternberg Fiedefomis (the seat of the head of the family).

The last Sternberg to live in Zasmuky was Leopold (1896 - 1957) who, as the eldest son, was responsible for the management of both estates. He married Cecilia Reventlow - Criminil, who, many years later, wrote "The Journey": a book filled with information about life in Bohemia before, during and after the second world-war.

In 1941, during the German occupation, both estates were run by a German "forced overseer". The SS took over Zasmuky and Leopold Sternberg with his family was forced to live elsewhere. In 1945 the properties were returned only to be confiscated in 1948 by the Communist Regime.

In 1949 the Castle of Zasmuky was given to the Czech Army and it became a store for weapons. In 1982, due to uncertain circumstances, the house caught fire, which spread through the whole of the northeast wing. The burnt out shell remained un- repaired and further deteriorated until 1992 when it was returned to Diana Phipps Sternberg, the daughter of the last owner. She is trying to manage the estate so that the profits can help rebuild the house, or at least preserve it for future generations.