Margin of error: ±3.31% Sample size: 874 Source:[6] South Dakota, a predominantly white and rural state in the Great Plains with a significant Native American population, was split near evenly between Clinton and Sanders in terms of geography and delegate count.

Senator Bernie Sanders kept the race close by winning the western portion, which is far more rural than the eastern half and tends to vote more Republican in presidential elections.

Sanders also carried the counties of Oglala Lakota, Jackson, and Bennett, which are part of the Pine Ridge Indian Reservation.

Another likely reason for the large amount of Native American support for Sanders was towards a controversial comment Secretary Clinton made in April after Donald Trump became the presumptive nominee where she stated, "I have a lot of experience dealing with men who sometimes get off the reservation in the way they behave and how they speak."

The remarks were considered offensive by many people, and likely benefitted Sanders (though Clinton appeared to do well among Native Americans in New Mexico the same day).