 He married Elizabeth Powell, daughter of Samuel Powell of Stanedge, Radnorshire, by whom he had a sole daughter and heiress Elizabeth Knight, who married Thomas Johnes (died 1780) of Llanfair Clydogau, MP for Radnorshire (1777–80).In the 1760s Thomas Johnes remodelled Croft Castle in the Rococo-Gothic style to the design of the architect Thomas Pritchard (d.1777).Their son and heir was Thomas Johnes II (1748-1816) of Croft Castle, MP, who adopted the additional surname of Knight (according to the mural monument he erected 1813/16 to his ancestors in the chapel of Croft Castle), a pioneer in the field of agriculture.