In 1940, a part of Dymsza’s lands were rented by the farmer Budreika. The Manor’s land was, nevertheless, seized and transferred to the State Land Fund. The Soviet government did not have time to implement its plans – to establish the Ilzenberg state farm or to allocated the lands to landless and land-poor peasants, for the Soviet-German war began, and Lithuania was occupied by German troops.
In 1944, after the Red Army dislodged German troops from Lithuania, the Soviet authority was restored and the seizure of lands of large landowners and farmers was proceeded; the state also took over the rest of land and property with no owners.
In May of 1948, the Ilzenberg Manor palace went to the collective farm “Aušra (Dawn)”. In 1950, “Aušra” was merged with collective farms “Laisvė (Liberty)”, “Keturi ežerai (Four Lakes)”, “Pažanga (Progress)”. In 1958, “Aušra” collective farm was re-organised to Onuškis state farm. Total farm area was 2,434.67 ha with 243 families. The farm was awarded the Honorary Order sign that was a significant acknowledgement in the days since the sign went to large and high-performing farms only. A terrace beside the Ilzeneberg Manor was equipped with a square, where song festivals, May Days, other celebrations and events took place in 1959-1966. The Ilzenberg Manor palace became the central gathering place in Onuškis surroundings. On 22 May 1963, by Decision of the Executive Committee of the Council of Working People's Deputies in Rokiškis district, the Ilzenberg park was added to the list of protected parks. The Onuškis state farm manager was appointed to be in charge of the park protection and proper care.
During the Soviet period (about 1966), the Manor passed to the disposal of Panevėžys plant “Ekranas (Screen)”. Under its management, the manor revived: restoration of the vast wine cellars started, the Manor changed both on outside and inside. Events were held in the Large Hall, living rooms were furnished. After Lithuania regained its independence, the Manor was transferred to the disposal of the state. During these years, the Manor stayed completely abandoned. In 2003, the Manor was privatized. Then again, the majority of the scattered buildings and lands of the manor were gathered into a single legal seat; currently the Ilzenberg Manor covers more than 220 ha of land in the surrounding areas.