Castletown Estate was purchased in 1802 by Robert Mounsey. In 1809 Castletown House was built by distinguished architect Peter Nicholson whom whilst in the area remodelled Corby Castle and over looked the erection of the Court Houses in Carlisle. Built in the Grecian style and completed in 1811 this well proportioned mansion stands magnificantly within the grounds of the Castletown Estate. The house was listed as a Grade II building in 1957.
Castletown House has been occupied by family members, sailors, soldiers and lawyers.
The house itself within the same boundaries as the parish of Rockcliffe was held from the king by Hugh de Morvill (the Lord of Burgh), who also built a castle on Burgh Marsh in which King Edward the First died.