The Collaborative International Dictionary of English v.0.48:

Sacs \Sacs\ (s[add]ks), n. pl.; sing. Sac. (Ethnol.)
   A tribe of Indians, which, together with the Foxes, formerly
   occupied the region about Green Bay, Wisconsin. [Written also
   Sauks.]
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Sauks \Sauks\, n. pl. (Ethnol.)
   Same as Sacs.
   [1913 Webster]