Sir Henry St John Carew St John-Mildmay, 4th Baronet (15 April 1787 – 17 January 1848), of Dogmersfield Park, Hampshire, was an English politician.
He was the son of Sir Henry St John-Mildmay, 3rd Baronet of Dogmersfield Park and educated at Winchester School (1798-1802) and Christ Church, Oxford (1805).
He was a Member of Parliament (MP) for Winchester 1807–1818 and Mayor of Winchester for 1808.He succeeded his father in the baronetcy on 11 Nov.
1808.
He married twice; firstly, in 1809, Charlotte, the daughter of Hon.
Bartholomew Bouverie, with whom he had a son and secondly, in 1815, in Württemberg, Harriet, a second daughter of Hon.
Bartholomew Bouverie and the widow of Archibald Primrose, 4th Earl of Rosebery, with whom he had eloped and had a further 3 sons.
His second wife eventually left him and, plagued by financial problems, he shot himself on 17 January 1848.