Best way to find out if my Great great grandfather is really a Native Amercan?

Question:

Best way to find out if my Great great grandfather is really a Native Amercan?

the story gose that my great great grandfather was Native Amarcan and livied In the white commuaty after he married a white woman. He use the name Beaver which was my grandmothers maiden name. Grandmother never said when He was born or what his wifes name was. She didn't know his place of birth or the date of birth. She told me he was from the Blackfoot tribe, but told my sister he was from some other tribe. We never did find out anything other than that. We do know know that Grandmothers faimly was from Danville Ill. and surranding towns and mineing camps.

Best Answer - Chosen by Asker: The bureau of Indian Affiars, US Dept of Interior, might be a good place to start your search as they keep recordsof American Indians.

Blackfoots were in the Montana region