At the beginning of the reign of King Matthias Corvinus, Ernuszts were wholesalers and bankers in Buda. John I Ernuszt, nicknamed „Hampó", became king's regular banker and increased his wealth by lucrative and profitable business with the sovereign. For his banking services he earned many titles and estates as well, either buying the land from the king or receiving it as mortgage for money lent to him. On 20 November 1473 he was appointed Ban of Slavonia, receiving at the same time Međimurje County, the northernmost part of the territory, with its seat Čakovec. Therefore, he appeared in historical documents as John Ernuszt de Csáktornya. After his death on 3 March 1476, he was succeeded by his sons John II and Sigismund. While the latter became Bishop of Pécs,, the former stayed in his father's main Međimurje estate and served, together with George Kanizsai, as Ban of Croatia. In the meantime, brothers earned some additional estates, among which were Đurđevac and Molve. Francis Ernuszt, the son of John II, inherited all of the family possessions after his father's death in 1519. He was known for his participation in the Battle of Mohács on 29 August 1526, where he was among many Hungarian and Croatian nobles who lost their lives. He left two sons, John III and Caspar. The former died in 1537 leaving no children, and the latter was married to Ana, a daughter of Petar Keglević, Ban of Croatia. Caspar took part in many battles against the Ottomans, leading his banderium, a kind of military unit, and even counter-attacked the enemy in already occupied parts of Croatia and Slavonia. Nevertheless, Ottoman numerical superiority was decisive and Croats were forced to retreat more and more to the west and northwest. One of the ways used for population to flee lead through the Caspar's Međimurje County. He himself helped people by setting ferries on the Drava and Mura river which enabled the refugees to cross them and go further north to reach western Hungary, which was still not occupied. Since Caspar died in 1540 without issue, his family died out. His widow Anna attempted to retain all his possessions, even engaging her father's military crew, but King Ferdinand I Habsburg did not allow it. In the name of the king, Nikola Šubić Zrinski, the new Ban of Croatia, pushed the Keglevićs out of Međimurje by force.
