https://en.wikipedia.org/wiki/Cook_County,_MinnesotaNeighbouring Iron Range counties (Saint Louis and Lake) have been generally consistent Democratic since the New Deal though it swung Republican heavily in the 2016 election, but Cook County seems to have distinct voting patterns separate from them.
-Swung strongly Republican after Eisenhower with the only Democrat until 1988 to win being LBJ in 1964. Notably, Minnesotans Hubert Humphrey and Walter Mondale both failed to take the county nor did Carter in 1976.
-Swings strongly Democratic starting with Dukakis in 1988 and the only Republican victory in 2000 seems attributable to a high third-party vote.
-Unlike many other white rural counties, Hillary Clinton did not lose much county and most defections were third party rather than towards Trump.
Some of the quirks might be explainable by the Native American reservation but they form less than a tenth of the population.