(esp. during the U.S. westward migration) any region where one was likely to encounter Indians, esp. hostile Indians.
Based on the Random House Dictionary, © Random House, Inc. 2010.
Indian country or Indian Country
1. Indian Territory.
2. Federal reservation lands under Native American tribal jurisdiction.
The American Heritage® Dictionary of the English Language, Fourth Edition
Copyright © 2009 by Houghton Mifflin Company.
Native Appropriations had this to say about Dictionary.com's definition:
Of course, you still hear the phrase "Indian country" used in a negative sense. Often enough that I have a page devoted to the subject. The implicit definition is something like:
Below: An old mural depicting an outdated concept of Indian country. Note the Indians skulking behind rocks on the righthand side.