Idaho Territory Reduced in Size to Create Montana [otd 05/26]

On May 26, 1864, the U. S. Congress passed legislation that reduced the previously-massive Idaho Territory by creating Montana Territory and splitting off most of future Wyoming. President Lincoln signed the bill two days later. By this action, they solved one of the major problems with the original structure of Idaho Territory.
Original Idaho Territory.
Adapted from J. H. Hawley with future borders tinted in color.
When Congress created Idaho Territory in 1863 [blog, Mar 4], it encompassed today’s...