Innisfree is an island in Lough Gill, which is mainly in County Sligo but partly in County Leitrim.
Innisfree is by no means the largest island in Lough Gill. Church Island and Cottage Island are much larger. Wikipedia also names one called Beezie's Island, which was inhabited until 1951, but this does not appear to be named on Google Maps.
According to Wikipedia, there are about twenty islands in Lough Gill. I counted 17 on Google Maps, of which only Cottage Island, Church Island and Innisfree are named. All seventeen are in the Sligo part of the lough.
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