The title of Viscount Gormanston was created in the Peerage of Ireland in 1478, and is the senior Viscount of Ireland, as well as the bearer of the oldest vicomital title in the British Isles.

The Viscount bears the subsidiary titles of Baron Gormanston (1370) and Baron Loundres (1478) in the Peerage of Ireland and Baron Gormanston (1868) in the Peerage of the United Kingdom.

Barons Gormanston (1370)

• Robert Preston, 1st Baron Gormanston (d. 1396)
• Christopher Preston, 2nd Baron Gormanston (d. 1422)
• Christopher Preston, 3rd Baron Gormanston (d. 1450)
• Robert Preston, 4th Baron Gormanston (d. 1503) (became Viscount in 1478)

Viscounts Gormanston (1478)

• Robert Preston, 1st Viscount Gormanston (1435_1503)
• William Preston, 2nd Viscount Gormanston (d. 1532)
• Jenico Preston, 3rd Viscount Gormanston (1502_1569)
• Christopher Preston, 4th Viscount Gormanston (1546_1599)
• Jenico Preston, 5th Viscount Gormanston (1584_1630)
• Nicholas Preston, 6th Viscount Gormanston (1608_1643)
• Jenico Preston, 7th Viscount Gormanston (d. 1691)
• Jenico Preston, 8th Viscount Gormanston (1640_1700)
• Anthony Preston, 9th Viscount Gormanston (d. 1716)
• Jenico Preston, 10th Viscount Gormanston (1707_1757)
• Anthony Preston, 11th Viscount Gormanston (1736_1786)
• Jenico Preston, 12th Viscount Gormanston (1775_1860)
• Edward Anthony John Preston, 13th Viscount Gormanston (1796-1876)
• Jenico William Joseph Preston, 14th Viscount Gormanston (1837-1907)
• Jenico Edward Joseph Preston, 15th Viscount Gormanston (1879-1925)
• Jenico William Richard Preston, 16th Viscount Gormanston (1914-1940)
• Jenico Nicholas Dudley Preston, 17th Viscount Gormanston (b. 1939)