Oliver St John, 1st Earl of Bolingbroke (1580? – June/July 1646), known from 1618 until 1624 as 4th Baron St John of Bletso, was an English nobleman and politician.
St John was son and heir of Oliver St John, 3rd Baron St John of Bletso, by his wife Dorothy Reid, daughter and heiress of Sir John Rede or Reid, of Oddington, Gloucestershire. He matriculated from Peterhouse, Cambridge, in about 1595 and was admitted at Gray's Inn on 20 April 1597.
St John was in parliament, elected as member for Bedfordshire in 1601, and again in 1604. In 1604 he served on the committee appointed to discuss the change in the royal title. On 3 June 1610 he was made knight of the Bath at the creation of Henry Frederick, Prince of Wales. In September 1618 he succeeded his father; in the following year he sumptuously entertained James I at his house, and in 1620 he took his seat in the House of Lords. On 28 December 1624 he was created Earl of Bolingbroke (a manor that had belonged to the Beauchamp family, from which he was descended). He took his seat on 22 June 1625.
In December 1626 St John refused to contribute to the forced loan; but in 1638–9 he contributed towards the expenses of the Bishops' War. On 28 August 1640 he signed the petition of the twelve peers, attributing the evils of the day to the absence of parliaments, and urging Charles I to summon one. He remained with the Long Parliament in 1642 when Charles retired to York, and in February 1642–3 was named by the parliament lord lieutenant of Bedfordshire; in this capacity he took an active part in raising the militia and providing for the safety of the shire. In the same year he took the Solemn League and Covenant, and was appointed a lay member of the Westminster Assembly. On 10 November he was one of the commissioners named for the custody of the Great Seal. In 1645 he was excused attendance at the House of Lords, and he died in June or July 1646.