The Princely Palace now houses the permanent exhibition – The Counts of Celje. The Counts of Celje were one of the most influential noble families in the Slovenian lands in the Late Middle Ages. The Celje Counts were the focus of the museum since its beginnings; the museum carefully collected material remains, excavated by archaeologists at the Old Castle (Stari grad) in Celje and other locations. In 1956, the skulls of the Celje Counts – safely guarded in the Minorite church in Celje, the former tomb of the counts – were transferred to the museum. Due to lack of space, the synoptic exhibition the Celje Counts, set up in 1999, was stored in a depot for a few years. The Princely Palace is the new exhibition grounds for the presentation on the Celje Counts.
The beginnings of the Celje Counts reach back into the period of the free lords of Žovnek, their family seat being the Žovnek Castle in Lower Savinja Valley. By the year 1333, the Žovnek lords inherited the Huenburg property in Savinja Valley, their seat now being in Celje. The accumulation of feudal estates and the establishment of political connections reinforced Žovnek's status to such a degree that the emperor Louis the Bavarian elevated them to the status of the counts of Celje. Charles IV of Luxembourg bestowed them the same status. The foundation of their power was the vast property in Styria, Carinthia, and Carniola.
The House of Celje experienced the summit of power during the reign of Herman II; due to his desire to become liberated from the hegemony of the House of Habsburg, he established close connection with the Hungarian king Sigismund of Luxembourg in 1396, who later became the German and Bohemian king, as well as the Holy Roman emperor. The Celje Counts acquired a plethora of territories and titles in the area of today's Croatia. Herman II became the Slavonian, Croatian, and Dalmatian Ban (civil governor); governor of the Croatian diocese with the right to bestow the title of Vicar; moreover, he was a close member of Sigismund Luxembourg's council. During their peak of power, the House of Celje established family relations with the Houses of Hungary (Barbara of Celje), Poland (Anne of Celje), Serbia (Ulrich II), and Bavaria (Herman III).
Herman II's goal of attaining power, for which he spent five decades, was achieved when Sigismund of Luxembourg elevated Frederick II and Ulrich II of Celje to the status of stately princes in Prague in 1436. Their lordship over Celje and Sternberg-Ortenburg properties became the independent principality of Celje, in which they obtained the right to mint their own money as well as having their own provincial court for the nobility (in German Landschrannengericht). At that point, the Celje Counts stood on an equal footing with the Habsburgs. Soon after their elevation to the status of princes, the Houses were engaged in a family feud – the Celje Counts became a serious threat to the interests of Habsburgs concerning Inner Austria. The peace treaty between the two Houses, finalized in 1443, enabled the House of Celje to preserve the princely status; however, the princely rights were taken away from them, which spelt the end of the initial formation of the independent land of Celje. The most important document regarding the compromise between the Houses was the contract of mutual inheritance, which later enabled the Habsburgs to acquire all of the property of Celje within the Holy Roman Empire.
Henceforth, the House of Celje directed their political ambition towards Hungary, in which Ulrich II managed to acquire the title of regent in 1456 for the Hungarian king Ladislaus the Posthumous. The high title, which the noble Ladislaus Hunyadi also fought for, simultaneously brought imminent death to the last male descendant of the Celje family. Within a year, the Hunyadi henchmen murdered Ulrich II of Celje.
The House of Celje was the last important medieval dynasty which rose to the heights of European aristocracy. Their princely palace in Celje was, besides Trieste, the only location in the lands of Slovenia where the European cultural and artistic streams flew.
In less than a century, the name of Celje was firmly stamped into the political sphere of the Central European area. The Celje Counts approved of many cultural creations of their time. They were the founders of monasteries, and were known for their church donations; they were also actively engaged in building and reconstructing castles, which they owned more than a hundred at the height of their power. Numerous architectural monuments of the late Middle Ages within and outside today's borders of Slovenia are connected with the names of the Counts.
The Celje Counts are still part and parcel of the collective memory of Slovenians. With the help of literature, various genres, and contributions of amateur and scholarly writers, the dramatic life stories of certain Celje family members have survived for the last 500 years – no other Slovenian noble family can claim such an achievement. Throughout the centuries, there has been a persistent notion about the affluent and uncomprising family, willing to go to extreme lengths to reach any goal; in the 19th century, there was also the historical myth about the Celje Counts as the first bearers of Slovenian nationality.