Viscount Sarsfield, of Kilmallock, was a title in the Peerage of Ireland.
It was created in 1627 for Sir Dominick Sarsfield, 1st Baronet, Chief Justice of the Irish Common Pleas.
The second Viscount converted to the Roman Catholic faith, and is chiefly remembered for sheltering his cousin William Tirry, the martyr.
The titles were forfeited in 1691 by the fourth Viscount for his part in the Williamite war in Ireland.
As often at the time, the family was divided in religion: the first Viscount was a Protestant, but the second and fourth were Roman Catholics.