Thomas Dillon, 4th Viscount Dillon

Thomas Dillon, 4th Viscount Dillon (1615–1672) was an Irish peer.

In 1630 he converted to Protestantism and was received into the Protestant Church of Ireland when he succeeded his nephew as Viscount Dillon. He subsequently took his seat in the Irish Parliament.

In February 1641, on the way to meet Charles I of England he and his brother in law Theobald Viscount Taaffe, were seized at Ware by order of the English House of Commons. They escaped a few months later and joined the King at York. Upon Dillon's return to Ireland, he was made Lieutenant-General, and was appointed President of Connaught, a position he was to hold jointly with Henry Wilmot, 2nd Viscount Wilmot. He was briefly one of the Lords Justices for Ireland.

Following the outbreak of the Irish Rebellion 1641, the rebel nobility established a Supreme Council of 25 men in November 1642, of which Dillon was one of the 6 members from Connacht.

On 6 December 1646 he was received back into the Roman Catholic Church by Nuncio Rinnuccini at St. Mary's Cathedral, Kilkenny. He was mentioned several times in the January 1648 treaty between the Irish Confederates and Ormonde as "Thomas lord viscount Dillon of Costologh".

He commanded a division of Ormonde's army that was defeated in the Battle of Rathmines before Dublin by the Parliamentary leader, General Jones, in 1649.

Dillon's estates were confiscated by the 1652 Cromwellian Settlement, and he and his family lived in exile on the Continent until the Restoration. In 1663 most of his extensive landed property was restored by the Act of Settlement 1662, and several high offices in the state were conferred upon him, including that of Custos Rotulorum of Westmeath.

On 3 January 1667 a Warrant written from Dublin Castle was sent to Dillon. It related to the pay and provisioning of men, Viscount Dillon had earlier been appointed to raise for special service in the province of Connacht.

He died about 1672. The family appear to have had a house in Winetavern Street, Dublin, as his wife and one of his sons died there, and were buried in St. James's churchyard.