Grønnessegaard is a manor house and estate located just east of Hundested in Halsnæs Municipality, Denmark, some 50 kilometres (31 mi) northwest of Copenhagen.

Johan Frederik Classen and his partner Just Fabritius had established the nearby Frederick's Works arms factory in 1756.

The manors produced food for the workers at his factory and at the same time played an important role as a labour reserve.

Det Classenske Fideicommis ceded Frederick's Works, Arresødal and Grønnessegaard to Prince Charles of Hesse-Kassel in return for the payment of 7,000 Danish rigsdaler to the foundation.

Prince Carl of Hessen-Kassel was married to Princess Louise of Denmark, a sister of Christian VII.