What states in the US have the highest population of Native Americans?

687,400
The American Indian and Alaska native population in California as of July 1, 2004, the highest total of any state in the nation. California was followed by Oklahoma (398,200) and Arizona (322,200). About 6,400 American Indians and Alaska natives were added to Arizona's population between July 1, 2003, and July 1, 2004. That is the largest numeric increase of any state in the nation. Florida and Texas added 5,300 and 4,500, respectively.

About 1 in 5
The proportion of Alaska's population identified as American Indian and Alaska native as of July 1, 2004, the highest rate for this race group of any state in the nation. Alaska was followed by Oklahoma and New Mexico (11 percent each).

This information comes from the US Census Bureau:

http://www.census.gov/Press-Release/www/releases/archives/facts_for_features_special_editions/005684.html