John Olmius, 1st Baron Waltham

John Olmius, 1st Baron Waltham (18 July 1711 – 5 October 1762), of New Hall, Boreham, Essex, was a British landowner and Whig politician who sat in the House of Commons between 1737 and 1762.

Background Olmius was the only son of John Olmius, of Braintree, Essex, Deputy Governor of the Bank of England, and his wife Elizabeth Clarke, daughter and heiress of Thomas Clarke, a London merchant. He was the grandson of a wealthy Dutch merchant who had settled in England. He acquired New Hall near Boreham, Essex, in 1737.

Political career Olmius was returned to Parliament as one of four representatives for Weymouth and Melcombe Regis at a by-election on 10 March 1737. At the 1761 British general election, he was returned for Weymouth and Melcombe Regis for a second time.

Family Lord Waltham married Anne Billers, daughter and heiress of Sir William Billers, of Thorley, Hertfordshire, Lord Mayor of London, in 1741. They had one son and a daughter. He died in October 1762, aged 51, and was succeeded in the barony by his only son, Drigue, on whose death in 1787 the title became extinct.