The so-called Upper Castle (Oberburg) comprises a rectangular plaza as main square which is surrounded two rows of houses, and into the limestone a 57 m (187 ft) deep water well was carved.

In 1583 and 1585 it was replaced by Vogt Vogel by a three-story building, which largely corresponds to the today's northern palace wing.

The Habsburgs mortgaged the castle and town several times,[4] and in 1407 the so-called Herrschaft Regensberg was acquired by the city of Zürich.

On 13 March 1798 the French revolutionary troops forced the council of the city republic of Zürich to abdicate, and the country bailiwicks were dissolved.

After the end of the short-lived Helvetic Republic, Regensberg became the district capital, and the castle was the seat of the cantonal authorities, and in the main building there was the county jail until 1863.

[2] In 1883 the charity Förder-Stiftung für Kinder und Jugendliche der Stiftung Schloss Regensberg was founded to establish the present special needs school for children.

[8] The so-called Hunfried document of 1044 AD mentions among others a witness named Lütold of Affoltern who is suspected as the builder of the Alt-Regensberg Castle on the border between Regensdorf and Zürich-Affoltern around 1050 AD, and Lütold I von Regensberg was mentioned as the first holder of the family's name around 1088.

Other assets and rights were in the Limmat and Reppisch valleys, in Zürcher Oberland, in the Pfannenstiel area, also sporadically in the present Thurgau and north of the Rhein river and on Bodensee lake shore.

Two monastic foundations date back to the House of Regensberg: Around 1130 Lütold II and his wife Judenta and his son Lütold III founded the Fahr Abbey, and with the foundation of Rüti Abbey in 1206 the family probably secured lands of the first extinction of the Alt-Rapperswil family around 1192.