The Connachta were a group of prehistoric and medieval Irish dynasties who gave their name to the province of Connacht (Irish Cuige Chonnacht, "province of the Connachta"). They were named after their supposed descent from the legendary king Conn Cétchathach.
The use of the word cuige, earlier cóiced, literally "fifth", to mean "province", implies the existence at some point in prehistory of a pentarchy, whose five members were the Connachta, (Connacht) the Ulaid (Ulster), the Laigin (Leinster), Mumu (Munster), and probably Mide (Meath), a central province whose name survives in Counties Meath and Westmeath, although the original Mide was more extensive than those counties.
Some early texts divide Ireland into two halves, Leth Cuinn ("Conn's half") in the north and Leth Moga ("Mug [Nuadat]'s Half") in the south, a state of affairs said to have existed at the time of Conn and his Munster rival Mug Nuadat. However, this is probably a projection back into prehistory of the medieval political dispensation, under which the Connachta and their offshoot, the Uí Néill, controlled most of the northern half of the island.
Scholars differ over whether the Connachta originated in the east midlands, in region of Tara, and expanded westwards into the province that now bears their name, or originated in the west and expanded into the midlands.