It has an Irish round tower, and the ruins of several small churches, as well as four high crosses and a holy well.

Coffins and mourners are transported the short distance from County Clare in small boats.

The second monastery, a famous school of learning, was founded by St. Caimin (d. 653), who was Bishop-Abbot of Inis Cealtra and possibly the first Bishop of Killaloe.

Marcán, brother of Brian Boru, was Bishop-Abbot of Tuamgraney and later Inis Cealtra until his death in 1003.

In 1849, the island was transferred to Galway as part of Griffith's Valuation, which was mandated to eliminate detached portions of counties.

However, in 1899, the district electoral division containing both the island and adjoining mainland was transferred from Galway to Clare under the Local Government (Ireland) Act 1898.

Old Ordnance Survey maps mark it as "Garaidh Mhichaeil" (Michael's garden) it was most likely a cillín, a burial ground for unbaptised children.

See Annals of Inisfallen AI922.2 Tomrair son of Elgi, a Jarl of the foreigners, on Luimnech (the Lower Shannon), and he proceeded and plundered Inis Celtra and Muicinis, and burned Cluain Moccu Nóis; and he went on Loch Rí and plundered all its islands, and he ravaged Mide.