In the years after the Civil War, the northern plains and Rockies saw considerable new settlement and development. The Johnson mapmaking firm from New York issued a series of maps with modifications each year reflecting the changes in the area.
The discussion of creating a territory in the area that became Wyoming in 1868 had started earlier, and this map of 1865 shows Wyoming, even though it would not officially exist for another two years. The map shows some of the interesting features of the borders in this rugged part of the country. The southern part of Wyoming’s western border is drawn at the 110 degree longitude line (this was moved west to the 111 degree line in 1868). The northern border was determined by the Montana border, which ran west along the 45th parallel until it reached 111 degree longitude, whence it dropped to 44 degree 30 minutes, and then due west until it intersected the continental divide, which was Idaho’s new eastern border. This left an odd, finger shaped area south of Montana and north of Idaho making up Wyoming’s northwest corner, shown prominently here. Interestingly, when Wyoming was officially created as a territory, the western border went straight along the 111 degree line, and this ‘gore’ reverted back to being part of Dakota even though it was totally separated from the rest of the territory by Wyoming. It remained part of Dakota until 1873.