The title of Earl of Ardglass was created in the Peerage of Ireland in 1645. The Earl held the subsidiary titles of Baron Cromwell and Viscount Lecale (1624). It became extinct in 1687.

Earls of Ardglass (1645)

• Thomas Cromwell, 1st Earl of Ardglass (1594-1653)
• Wingfield Cromwell, 2nd Earl of Ardglass (1622-1668)
• Thomas Cromwell, 3rd Earl of Ardglass (1653-1682)
• Vere Essex Cromwell, 4th Earl of Ardglass (1623-1687)