Haddon Mirk is an extensive area of marsh, swampland and forest fed by the River Iralell, a major tributary of the Erinin. It is bordered by the Spine of the World to the east and the Erinin to the west. It stretches as far as the border of Tear in the south and almost to the Maraside Mountains in the north.
Haddon Mirk appears to be mostly uninhabited due to its unpleasent climate and terrain. However, its vast size makes it an attractive hiding place for bandits and rebels. After Rand al'Thor captured Tear, the Tairen rebels opposed to him and led by the High Lord Darlin Sisnera fled into Haddon Mirk. Rand later won Darlin's allegiance and made him King of Tear. The rebels loyal to Darlin returned peaceably to Tear.
The nation of Mar Haddon once existed in this region, but it fell several centuries ago. Tear and Cairhien both attempted to annex its territory, but lacked the manpower to hold the region. Tear's northern border did extend permanently as a result of this, however.