Nord Stern’s original application for Region status in March of 1959 listed its area pretty much as it is today, all of Minnesota and the western half of Wisconsin. From this letter and another in the Nord Stern file at the PCA National Office, at some point North Dakota and South Dakota were added to the Nord Stern Region. Based on this letter, the Dakota Region was carved out sometime after August 1961 and as it continues to this day.
Ironically, I was Dakota Region President in 1980 and 1981 when I lived in Bismarck.