In 1790 St John succeeded his wife's great-uncle Carew Hervey Mildmay to Marks Hall, Essex and Hazelgrove, Somerset and took the additional name of Mildmay. In 1796 he also succeeded his wife's aunt Anne, widow of Sir William Mildmay, 1st Bt., to Moulsham Hall, Essex.[2]
Paulet (8 Apr 1791-19 May 1845); married Anna Maria Wyndham Bouverie, daughter of the Hon. Bartholomew Bouverie MP. They had four children.
Capt. George William (20 Apr 1792-14 Feb 1851); married Mary Baillie, daughter of Peter Baillie MP for Inverness Burghs. They had a son, and daughter.
Humphrey (11 Jul 1794-9 Aug 1853); married first the Hon. Anne Eugenia Baring, daughter of Alexander Baring, 1st Baron Ashburton. After her death he married Marianne Frances Harcourt-Vernon, daughter of Granville Harcourt-Vernon MP. He had two sons with Anne, and three daughters with Marianne.
Capt. John Francis (8 Dec 1795-1 Sep 1823); unmarried.
Capt. Edward (7 Jul 1797-16 May 1868); married first Marianne Catherine Sherson, and together had four children. They divorced in 1830, and five years later he married Frances Lucy Penelope Percival. They had one daughter.
Rev. Walter (12 Oct 1798-31 Jul 1835); married Kitty Anne Warde. No known issue.
Ven. Carew Antony (2 Feb 1800-13 Jul 1878); married the Hon. Caroline Waldegrave, daughter of Adm. William Waldegrave, 1st Baron Radstock. They had two daughters.