Earl of Roscommon

The fifth Earl was a professional soldier, politician and courtier: he was friendly with Samuel Pepys, who refers to him several times as "Colonel Dillon" in his famous Diary.

After the death of the tenth Earl, there were two prolonged investigations by the Irish House of Lords during the 1790s to ascertain the legitimacy of his son Patrick, against the rival claim by Robert Dillon, a descendant of the seventh son of the first Earl and the next male heir in line.

The House of Lords decided against Francis Stephen Dillon (d 1840[2]), an inmate of a debtors' prison who dubiously claimed descent from the third son of the first Earl.

[4] The Dillon family held substantial lands in Meath, Westmeath, Longford and Roscommon.

This family has three noble branches: The Viscounts Dillon, the Earls of Roscommon and the Barons Clonbrock.