Abraham Lincoln proclaimed the first national Day of Thanksgiving on October 3, 1863, to be observed on the last Thursday in November. Governor Newton Edmunds of Dakota Territory followed suit with this proclamation on October 26, 1863.

Thanksgiving Proclamation, 26 October 1863, Newton Edmunds, Governor
Official Papers, Office of the Governor, Dakota Territory, Manuscript Series 30076, Box 1, Folder 11.
Preserved in State Archives and Historical Research Library, State Historical Society of North Dakota, Bismarck, North Dakota.