This family name is closely connected with Co. Clare and is the most important sept of Dál gCais - ancient Irish chieftains dating back to prehistoric times - after the O'Briens of this county. The name comes from Mac Conmara, meaning son of the hound of the sea, Co. Clare being on the Atlantic coast. Several castles have connections with the MacNamaras, including Bunratty Castle, near Shannon airport. The MacNamaras owned Bunratty Castle before it passed to the O'Briens. Knappogue Castle, nearby, was built by a MacNamara in 1487. Also in this part of Co. Clare is Cratloe Castle, built by the MacNamaras in 1610.

The most important site in Co. Clare associated with the MacNamaras is Quin Abbey, six miles east of Ennis. The abbey was founded by Sioda MacNamara in 1402 and contains tombs of the MacNamara family.

Francis McNamara, who died in 1945, owned the Falls Hotel in Ennistymon, Co. Clare, a delightful village with some shop signs still in Irish and the ever present falls. He was the father of Caitlin, who married the drunken but melodic Welsh poet Dylan Thomas.