Mutton Island is the largest island off the Clare coast. Quilty is the nearest mainland village.
Samuel Lewis writing in 1837 describes it as; "half a mile from the shore, on the western coast…It lies off that part of the coast which, from its rocky and dangerous character, is called the Malbay, and contains 210 statute acres of excellent land for feeding oxen and sheep, particularly the latter"
Hence the name "Mutton Island" from the fine flavour of the mutton.
According to the "Annals of the Four Masters" the island was once called Fitha Island and it formed part of the mainland until the day "the sea swelled so high that it burst its boundaries, overflowing a large tract of country, and drowning over 1,000 persons."
This happened on March 16th, 804. Some reports describe it as an earthquake, others as a tidal wave when "the sea divided the island of Fitha into three parts."
These three islands are Mutton Island, Inismattle (or Illanwattle) and Roanshee (or Carrig na Ron).
Lewis gives this account of Mutton Island; "On its shores are some curious natural caves, formerly used by smugglers for storing contraband goods. Here are an old signal tower and the ruins of an ancient structure, said to have been founded by St. Senan of Inniscattery."
Reference: http://www.clarelibrary.ie/eolas/coclare/places/mutton_island.htm