"The Lake Isle of Innisfree" is a twelve-line poem composed of three quatrains written by William Butler Yeats in 1888 and first published in the National Observer in 1890. It was reprinted in The Countess Kathleen and Various Legends and Lyrics in 1892 and as an illustrated Cuala Press Broadside in 1932.

Answer this question: who wrote about the idyllic'isle of innisfree'? Let's give stream of consciousness first:
This is the relevant information: "The Lake Isle of Innisfree" is a twelve-line poem composed of three quatrains written by William Butler Yeats in 1888 and first published in the National Observer in 1890.
So, the final answer is William Butler Yeats.