Situated 20 miles (32 km) south of Galway Bay, 1 mile (1.6 km) off Seafield Harbour, in County Clare, this large private island is covered in grasslands and contains a freshwater lake and several springs.

The island rises from sea level on the eastern side to a height of 110 feet (33.53 m) on its western end. Mutton Island has a long history. In 548 AD, St. Senan constructed a church there. In the 1700s, the island was home to wine and tobacco smugglers. Inhabited until 1948, Mutton Island contains the ruins of 2 cottages and an oratory, as well as a graveyard and several walled fields.

The nearby mainland and the island itself are steeped in history and folklore and it is believed that the "Children of Lir" spent their last 300 years on this island, now buried in the neighbouring locality. This is the reason why the " Children of Lir" is a symbol for the island's nearest town.

The island has been inhabited since pre-history, exhibited by traces of potato plots, a well, and most amazingly, a curious Pagan or Early Christian 6 foot tombstone with hieroglyphic inscriptions standing in absolute pristine condition, despite centuries of Atlantic weather conditions.

Up until the turn of the last century, the island had inhabitants, but they left at the beginning of the 20th century and the island is now uninhabited. To this day, their lifestyle can be easily identified by the remaining ruins of a cluster of old stone houses on the centre of the Island. There are six derelict houses and on the inside of one of the houses, there is still a doorway leading from the livingroom to what they called " the upper room", the bedroom. In its day, mothers gave birth to future islanders.

Standing at the doorway, one can see the high cliffs of Achill lying fifteen miles south across the sea. To the east, a boat is required to cross to the mainland, Blacksod Bay, near Belmullet. To the north, the view is a vast panorama commencing at the lighthouse on Eagle Island and then as one's eye moves eastwards, the hills of Erris stretching down to Ballycroy and continuing on to Achill Sound and Achill Island itself with its two peaks surveying all, two hundred and seventy degrees of sheer grandeur.

The island holds an important breeding population of Grey Seal and is also of orthinological interest for its colonies of breeding seabirds such as Great Black Backed Gull, Cormorant and Storm Petrel. Seal Islands are also considered an excellent wintering ground for internationally important numbers of Barnacle Geese.

The narrow strait between the two islands is called Leamabradaun, meaning ''passageway of the Salmon''. Clear proof of this fact is the constant presence of a group of seals which inhabit the rocks surrounding the two islands.