Did South Dakota Annex Canada East in 1915?

This may look I made it up, but it is right off the Ancestry.com website as of 12:49 PM central time today.

The 1915 South Dakota State Census contains information from "Canada East." Yes, Canada East.

This is an unaltered image.

Apparently someone at Ancestry.com is using an altered map. I hate it when I realize there's some United States history I don't know.

This appears to be the same database that FamilySearch has had on their site for some time. That database indexes the cards created from the 1915 South Dakota state census.