The Territory of Wyoming was an organized incorporated territory of the United States that existed from July 25, 1868, until July 10, 1890, when it was admitted to the Union as the State of Wyoming. Cheyenne was the territorial capital. The boundaries of the Wyoming Territory were identical to the modern State of Wyoming.
Because of Wyoming's location at the intersection of the Louisiana Purchase, the Oregon Country, and the Mexican Cession, the land which became Wyoming has a complicated history of territorial relationships. Portions of the territory which eventually fell under Wyoming's jurisdiction were at various points associated with Washington, Oregon, Idaho, Dakota, Nebraska and Utah, and had previously belonged to the independent states of Great Britain, France, Spain, Mexico, and Texas.
The portion of the Wyoming Territory east of the continental divide was acquired by the U.S. in the 1803 Louisiana Purchase and organized into the Nebraska Territory in 1854. In 1861, the northern half of the Nebraska Territory, including the northeastern portion of future Wyoming Territory became part of the Dakota Territory (left), while the southeastern portion remained with Nebraska, forming an extended Nebraska "panhandle" which included the settlement of Cheyenne. In 1863, the Idaho Territory was formed; it included the entirety of the modern states of Idaho and Montana and almost all of modern Wyoming save the southwest corner.
The portion of the Wyoming Territory west of the continental divide and north of the 42nd parallel was originally part of the Oregon Country, which was organized into the Oregon Territory in 1848; when Oregon entered the union as a state under its present boundaries in 1859, this land became part of the Washington Territory (although its eastern part had been granted to the Nebraska Territory in 1854 (right). The Idaho Territory subsumed this land as well in 1863.
The southwestern corner of what became the Wyoming Territory, south of the 42nd parallel, became part of the United States with the 1848 Mexican Cession. An eastern section of this was once claimed by the Republic of Texas. In 1851, the portion of this land west of the continental divide was made part of the Utah Territory, and, with the organization of the Colorado Territory in 1861, most of it was transferred to the Nebraska Territory (left) and subsumed into the Idaho Territory in 1863. A small corner of Wyoming remained part of Utah until the creation of the Wyoming Territory in 1868.
In 1864, with the formation of the Montana Territory, the southeastern section of the Idaho Territory (most of modern Wyoming) became briefly part of Dakota Territory once again (right), although a strip of land along the western border of what would become Wyoming remained part of the Idaho Territory.
The Territory of Wyoming was created by Act of Congress on July 25, 1868. At the time of its formation, it took land from the Dakota, Idaho, and Utah Territories. It was admitted to the Union as the 44th state on July 10, 1890.
 See also
- Bibliography of Wyoming history
- American Civil War, 1861–1865
- California Trail
- Compromise of 1850
- First Transcontinental Railroad
- Fort Laramie
- Historic regions of the United States
- History of Wyoming
- Mexican-American War, 1846–1848
- Mormon Trail
- Oregon Trail
- Territorial evolution of the United States
- Territories of Spain that encompassed land that would later become part of the Territory of Wyoming:
- Territory of France that encompassed land that would later become part of the Territory of Wyoming:
- Louisiane, 1682–1764 and 1803
- Territory of Mexico that encompassed land that would later become part of the Territory of Wyoming:
- Santa Fé de Nuevo México, 1821–1848
- Territorial claim of the Republic of Texas, 1836–1845
- U.S. territories that encompassed land that would later become part of the Territory of Wyoming:
- Louisiana Purchase, 1803–1804
- District of Louisiana, 1804–1805
- Territory of Louisiana, 1805–1812
- Territory of Missouri, 1812–1821
- Adams-Onís Treaty, 1819
- Former territorial claim of the Republic of Texas, 1845–1850
- Mexican Cession, 1848–1850
- Territory of Oregon, 1848–1859
- State of Deseret, 1849–1850 (extralegal)
- Territory of Utah, 1850–1896
- Territory of Nebraska, 1854–1867
- Territory of Washington, 1853–1889
- Territory of Jefferson, 1859–1861 (extralegal)
- Territory of Dakota, 1861–1889
- Territory of Idaho, 1863–1890
- US state created from the Territory of Wyoming:
- State of Wyoming, 1890
- U.S. congressional delegates from the Territory of Wyoming