In 1861, Dakota Territory included portions of present-day Montana, Idaho and Wyoming. As each region became separate territories, it appeared that the borders of the three future states failed to join; leaving a triangular section between Montana, Wyoming and Idaho that still belonged to the Territory of Dakota. Land office maps from the 1860’s marked this area as almost 100 miles wide and 35 miles deep. On this day, Feb 11, 1873, the US Senate approved HR Bill No. 2593 adjoining this triangular remnant of Dakota Territory to Montana. President Grant signed the bill six days later.

Soon after, a partial survey of the area revealed that such an extensive area could not have existed. In the end, Montana acquired an area a mere four miles long and two miles deep where it touches Wyoming’s northwest corner. Most of the area lies within the boundaries of Yellowstone National Park.

Written by Christina Campbell

Sources:
Murray, Genevieve, “The “Lost” Dakota Territory” North Dakota History: Journal of the Northern Plains, Vol. 35, No. 1, 1968, pg 62-67
http://historical-county.newberry.org/website/Dakota_Territory/documents/DT_Consolidated_Chronology.htm

This text and audio may not be copied without securing prior permission from North Dakota Public Radio.