Where does “ダコタ” come from?

ダコタ (Japanese) comes from English Dakota, from Dakota dakhóta — ally.

Ancestry of “ダコタ”, step by step

Step	Language	Word	Meaning
1	English	Dakota	A member of the Dakota people; A Douglas DC-3...
2	Dakota	dakhóta	ally

ダコタ — Etymology, Origin & Word History | Etymology Explorer