The Brown Lands were located east of the Anduin to the south of Rhovanion, between the Emyn Muil and the southern borders of Mirkwood.

Until the Second Age, they were a garden land full of blossoms and fruit, tilled and cared for by the Entwives. Much of the knowledge of the Entwives was passed on to men and the fields and crops of the region were rich and bountiful.
However, at some time during the Second Age, the works of Sauron destroyed the living greenery, leaving a twisted desert land full of brown and withered plants and trees, with no hint of living green remaining.

The land remained that way from then on, and the Entwives were either destroyed with the lands, or else moved away, for they had never been seen since.