John Dalton married Mary Gage and carried out some modernisation of the building in 1823, replacing the front facade and adding corner turrets and embattled parapet. His son John died childless and the property passed to John Jnr's sister Elizabeth in 1837, who built a private chapel in the hall in 1854. On her death in 1861 she was succeeded by a distant cousin, Sir James Fitzgerald, who adopted the additional surname of Dalton. He died childless in 1867 without issue and his brother, Sir Gerald Dalton-Fitzgerald, succeeded to the property. Most of the contents of Thurnham were sold and the remainder transferred to the Dalton-Fitzgerald's Essex estate.
