Innisfree ain't the only island in town. Nope, the lake it's in (Lough Gill) actually has about twenty total. So what's so special about this one, Yeats? (Source.)
Yeats had quite the fascinating love life. Yep, we said it. He was in love with Irish Revolutionary Maud Gonne, who broke his heart and married another man. For more on this, see Shmoop's guide to Yeats's poem "No Second Troy."