The name alone raises questions. Deer were once a significant presence across Ireland's medieval landscape, kept in managed deer parks by Anglo-Norman lords and later by Gaelic chieftains who adopted the practice. An island bearing such a name suggests, at minimum, a long memory, and possibly a deliberate use of the land for enclosing or sheltering animals at some point in the distant past.

Lough Carra itself has a character quite distinct from the darker, peat-stained lakes more commonly associated with Connacht. Its waters sit over a bed of limestone marl, which gives the lake a pale, almost milky appearance in certain lights, and supports an unusual freshwater ecosystem. The wider area around the lake has strong literary associations, most notably with the novelist George Moore, who grew up at Moore Hall on the western shore and wrote about this landscape with close attention. Whether Deer Island figures in any documentary or archaeological record remains, for now, unclear, which makes it one of those genuinely opaque corners of the Irish landscape, a place where the name is older than any surviving explanation for it.