A stone house on the site of current Mheer Castle was first mentioned in 1314. It was probably built long before that, because the Lords of Mheer were already mentioned around 1100. In the 14th century the castle went to the Van Imstenraedt family through marriage. The castle stayed in this family until 1668, then it went to the De Loë family. They still own the castle.
The castle is situated against the slope of a hill and thus has a dry moat. From the original 14th century castle only wall fragments remain. This original castle probably consisted of three wings surrounding a courtyard with the fourth side closed by a curtain wall. The present bailey dates back to the 16th and 17th century.
The present castle was rebuilt, with the use of original wall fragments, on the medieval foundations in the 17th century. Also in later centuries, up until the 20th century, a lot of rebuilding took place.References:
Ängsö Castle was first named as "Engsev" in a royal charter by king Canute I of Sweden (r. 1167-1196), in which he stated that he had inherited the property after his father Eric IX of Sweden. Until 1272, it was owned by the Riseberga Abbey, and then taken over by Gregers Birgersson.
From 1475 until 1710, it was owned by the Sparre family. The current castle was built as a fortress by riksråd Bengt Fadersson Sparre in the 1480s. In 1522, Ängsö Castle was taken after a siege by king Gustav Vasa, since its owner, Fadersson's son Knut Bengtsson, sided with Christian II of Denmark. However, in 1538 it was given by the king to Bengtsson's daughter Hillevi Knutsdotter, who was married to Arvid Trolle.
In 1710, the castle was taken over by Carl Piper and Christina Piper. Ängsö Castle was owned by the Piper family from 1710 until 1971, and is now owned by the Westmanna foundation. The castle building itself was made into a museum in 1959 and was made a listed building in 1965. It is currently opened to visitors during the summers.
The castle is a cubical building in four stores made by stone and bricks. The lower parts is preserved from the middle ages. It was redecorated and expanded in the 1630s. The 4th storey as well as the roof is from the expansion of Carl Hårleman from 1740-41. It gained its current appearance in the 1740s.