Wyoming is a state in the western region of the United States of America. The easternmost section of the state is a region known as the High Plains due to its altitude above sea level, while the majority of the state is dominated by the mountain ranges and rangelands of the Rocky Mountain West. Wyoming is the least populous U.S. state. The United States Census Bureau estimates that the state population was 515,004 in 2006, a 4.3% increase since 2000. The capital and the most populous city of Wyoming is Cheyenne.
The region known today as the state of Wyoming was originally inhabited by several Native American groups. The name Wyoming is derived from the Delaware (Munsee) name xwé:wamənk, meaning "at the big river flat", originally applied to the Wyoming Valley in Pennsylvania. Although French trappers may have ventured into the northern sections of the state in the late 1700s, John Colter, a member of the Lewis and Clark Expedition, was probably the first white American to enter the region in 1807. His reports of the Yellowstone area were considered at the time to be fictional. Robert Stuart and a party of five men returning from Astoria discovered South Pass in 1812. The route was later followed by the Oregon Trail. In 1850, Jim Bridger located what is now known as Bridger Pass, which was later used by both the Union Pacific Railroad in 1868, and in the 20th century by Interstate 80.
Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, and on the west by Idaho. It is the tenth largest state in the United States in total area and is made up of 23 counties. From the north border to the south border it is 276 miles (444 km); and from the east to the west border is 375 miles (603 km).
The Great Plains meet the Rocky Mountains in Wyoming. The state is a great plateau broken by a number of mountain ranges. In the northwest are the Absaroka, Owl Creek, Gros Ventre, Wind River and the Teton ranges. In the north central are the Big Horn Mountains; in the northeast, the Black Hills; and in the southern region the Laramie, Snowy and Sierra Madre ranges.
The climate in Wyoming is generally a semi-arid continental climate (Köppen climate classification BSk) which is drier and windier in comparison to most of the United States with temperature extremes.