Muintir Eolais was the name of a people in the medieval part of Conmaicne Réin and Magh Réin (in present-day south Leitrim, Ireland) who gave their name to the area which is roughly coterminous with the current baronies of Leitrim and Mohill. The principal family of the Muintir Eolais was the Mac Raghnaill family, who built a medieval castle on the shores of Lough Rynn.
In Clonmacnoise monastery today there is a headstone to Odhrán Ua Eolais, scribe of Clonmacnois, who died in 994AD. The inscription translates as 'Pray for Odhrán descendant of Eolas'. Eolas had been chieftain of Magh Réin in circa 900AD. Thereafter the people in this area are commonly recorded as Muintir Eolais (people/descendants of Eolas), a name which over time was applied to their area.