The Fortúatha were "kingdoms not ruled directly by members of the dominant dynasty of a province".
Population-groups classed as fortúatha included the Calraige, Ciarraige, Corca Fhir Trí, Delbhna, Déisi, Gailenga, Grecraige, Luighne, Masraige and Setantii.
The status of each population-group could differ from one part of the island to another, with some fortúatha being class as aithechtúatha in other regions.
In Leinster, some reckoned among the fortúatha had previously held the provincial kingship.
Among the early medieval Irish were many notable people whose population-group were classed as fortúatha.