The island is home to a lighthouse, a ruined monastery associated with Saints Senan and Canir, an Irish round tower and the remains of an artillery battery.

The legend of "St Senanus and the Lady", as told in Thomas Moore's lyric, is founded on the fact that no woman was allowed on Inis Cathaigh.

[2] St Senan died in 560 and was buried in the abbey church of Inis Cathaigh on 8 March, on which day his feast is observed.

[8] Ivar of Limerick, the last Norse king of the city, along with two of his sons, was slain on Inis Cathaigh by Brian Boru in 977.

This was absorbed by the Diocese of Killaloe in 1189,[9] but was restored by Pope Innocent VI and continued as a separate see under Bishop Thomas (1358–68).

Its main armament consisted of six 24-pounder long guns arranged along the length of the curved D.[14] In 1842, after the salvaging the Windsor Castle, Inis Cathaigh was home to Shannon Estuary Pilots and their families.

The primary families of the island were the Brennan, Melican, Scanlan, McMahon, Costelloe, Hehir, Moran, Crotty, and Griffin.

[16] The river pilots were highly skilled mariners, using only native currachs (canvas boats) to reach incoming and outgoing ships.