The area of land declared as the land of the Santhals was called "Damin-i-koh." Here's the reason for this:

1. Damin-i-koh: This term refers to the hill and forest tracts, often hilly or undulating terrain. The Santhal Paraganas or Santhal Parganas in Jharkhand, India, was designated as a place for the Santhal tribal community. The term "Damin-i-koh" roughly translates to "the land of the hills" or "hilly terrain," which was the homeland of the Santhal people.

The Santhal Parganas were created as a separate administrative region to protect the traditional lands and rights of the Santhal tribal community, and it was officially designated as "Damin-i-koh" to reflect its geographic characteristics.

So, the correct option is [2].