The Wild

Our only map that specifically mentions the Wild as a location, the large-scale map shown in The Hobbit, gives it a distinct and exact western border running southwards slightly to the west of the Misty Mountains, so that Rivendell falls just within the Wild's western edge. It's evident from that map the northern Vales of Anduin and the northern parts of Mirkwood fell within the Wild, as did Erebor and Dale. No eastern or southern boundaries are marked, but they did likely exist. If we extend the marked Edge of the Wild southwards, it would incorporate Rohan and most of Gondor, which would hardly have counted as part of the 'Wild'. It seems reasonable to assume a correlation with Rhovanion, and possibly Rhûn beyond, but it's less clear whether Mordor or the Harad were counted as part of the Wild in its strictest sense.

In his unpublished index to The Lord of the Rings, Tolkien defines the Wild as 'uninhabited lands', which helps to clarify things a little. On this defintion, then, it seems that Gondor, Rohan and presumably Mordor would be excluded. This definition does not seem to require that a region be totally uninhabited to count as part of the Wild (as places like the Woodland Realm or Lake-town were explicitly within it).

The rather improbably exact Edge of the Wild appears in the endpaper map to The Hobbit. The line marked on that map does not in fact fit exactly onto the geography of The Lord of the Rings, but it was clearly intended to mark a point just to the west of the Ford of Bruinen on the way to Rivendell. The map above uses that as a point of reference.