UFO Map: Northern Plains
The oldest reports shown here in blue date from the 1800s through 1959. These seem to fan out in all directions from Chicago with a light sprinkling elsewhere. Some of those are "Great Airship" sightings as reported, perhaps fancifully in newspapers of the time.Violet spots (1960-1979) predominate elsewhere, especially North Dakota and parts of Montana near missile silos and Air Force facilities.
There is no simple explanation for these cases in Western Alberta and elsewhere.
The most recent events in Green, 1980 to present, are scarce and scattered here with one grouping near Minneapolis, MN.
Sightings in the Canadian "bread basket" seem out of proportion to the relatively small population, but see these State / Province sightings counts.