The oldest information about the residence in Starawieś is included in the inventory of the Węgrów estate prepared in 1619 by Jakub Nurzyński at the request of Janusz Radziwiłł, the Vilnius castellan (father of the Lithuanian equerry Bogusław Radziwiłł). These documents show that the palace was one of the elements of the so-called manorial complex, also consisting of a wooden manor house and separate baths, kitchen and outbuilding, as well as a farm. The residence, located on the border between Podlasie and the Crown, was defensive in nature, surrounded by a palisade reinforced with towers and a moat that has survived to this day. The palace was a three-story brick building with a ceramic roof and a tower with a clock on the second floor. The entrance was located in the axis of the front façade and led to a hall with stairs. The representative floor was covered with a beam ceiling. There were apartments of the prince and duchess, decorated with polychromes, with picture galleries (including portraits of princes Janusz and Krzysztof Mikołaj Radziwiłł) and a dining room with eight windows, occupying half of the floor.
The palace was renovated and modernized several times. A major reconstruction was carried out in the years 1655-61 thanks to the efforts of Prince Bogusław Radziwiłł. Two towers were added in the front corners, covered with spherical cupolas, and the roof was covered with tiles. The interior layout and arrangement have not changed. The inventory prepared during the reconstruction in 1659 by Władysław Starzyński and Jan Pękalski shows that the palace was equipped at that time, among others. in a triple fortification system, a double palisade and a moat. Thanks to these fortifications, it survived the Swedish wars unscathed.