Johann Adam von Grünewaldt began redesigning the heart of the manor in the second half of the 18th century based on his financial capability and the architerctural trends of the time. The early classical main stone building with baroque elements was finished in 1771. The main building originally had a rectangular plan and a high hipped roof. Later, the building underwent a major reconstruction and was supplemented by wings on its courtyard-side. The main building of Koigi Manor was fully renovated in 2008–2009 by the European Financial Stabilisation Mechanism and Koigi rural municipality, as a result of which you now have access to this timeless building with all modern amenities. The new courtyard of Koigi Manor is also open.