Carved from sections of Dakota, Utah, and Idaho territories, Wyoming Territory came into existence by act of Congress on July 25, 1868. The territorial government was formally inaugurated May 19, 1869. The first territorial governor, John A. Campbell, appointed by President Ulysses S. Grant, took his oath of office on April 15, 1869.
At the time of its organization, Wyoming had already been divided into four counties: Laramie, established January 9, 1867; Carter (later Sweetwater), established December 27, 1867; Carbon and Albany, December 16, 1868. These counties extended from the northern to the southern boundaries of the territory. Upon the organization of Wyoming Territory, a portion of Utah and Idaho, extending from Montana (including Yellowstone Park) to the Wyoming-Utah boundary, was annexed and named Uinta County. As the territory and later the state became settled, the following counties were carved from the original five until there are now twenty-three counties in Wyoming.
On July 10, 1890, the territory consisting of the thirteen counties was admitted into the Union as a State.