John St John, 12th Baron St John of Bletso

John St John of Northwood, 12th Baron St John of Bletso (15 November 1725 – 20 April 1767) was a British peer.

Biography St John was the eldest son of John St John, 11th Baron St John of Bletso and his wife Elizabeth Crowley, daughter of Sir Ambrose Crowley of Greenwich. He was educated at Winchester College and at New College, Oxford. He inherited the title of Baron St John of Bletso on the death of his father in 1757.

St John died at the age of 41 at Nice but was buried at Bletsoe.

St John married 13 December 1755 to Susanne Louise Simond, the daughter of Peter Simond, a wealthy French Huguenot merchant in London. She brought £20,000 to the marriage. married 31 March 1795, Henry Vaughan, physician extraordinary to the king. Charlotte St John (15 March 1763 – 24 July 1803), married Joseph Yates, esq.

Their eldest son, John Peter died aged just three and St John was succeeded in the barony successively by his second son Henry and his third son St Andrew. His widow died at Bath, Somerset in 1805 at the age of 80.