Wyoming ( (listen)) is a state in the Mountain West subregion of the Western United States. The 10th largest state by area, it is also the least populous and least densely populated state in the contiguous United States.Wyoming is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the south. Its population was 576,851 at the 2020 United States census, making it the least populated U.S. state. The state capital and the most populous city is Cheyenne, which had an estimated population of 63,957 in 2018.Wyoming's western half is covered mostly by the ranges and rangelands of the Rocky Mountains, while the eastern half of the state is high-elevation prairie called the High Plains. It is drier and windier than the rest of the country, being split between semi-arid and continental climates with greater temperature extremes. Almost half of the land in Wyoming is owned by the federal government, generally protected for public uses. The state ranks 6th by area and fifth by proportion of a state's land owned by the federal government. Federal lands include two national parks (Grand Teton and Yellowstone), two national recreation areas, two national monuments, several national forests, historic sites, fish hatcheries, and wildlife refuges.

Indigenous peoples inhabited the region for thousands of years. Historic and current federally recognized tribes include the Arapaho, Crow, Lakota, and Shoshone. During European exploration, the Spanish Empire was the first to "claim" Southern Wyoming. With Mexican independence, it became part of that republic. After defeat in the Mexican–American War, Mexico ceded this territory to the U.S. in 1848.

The region was named "Wyoming" in a bill introduced to Congress in 1865 to provide a temporary government for the territory of Wyoming. It had been used earlier by colonists for the Wyoming Valley in Pennsylvania, and is derived from the Lenape language Munsee word xwé:wamənk, meaning "at the big river flat".Historically, European Americans farmed and ranched here, with shepherds and cattle ranchers in conflict over lands. Today Wyoming's economy is largely based on tourism and the extraction of minerals such as coal, natural gas, oil, and trona. Agricultural commodities include barley, hay, livestock, sugar beets, wheat, and wool. It was the first state to allow women the right to vote and the right to assume elected office, as well as the first state to elect a female governor. Due to this part of its history, its main nickname is "The Equality State" and its official state motto is "Equal Rights". It has been a politically conservative state since the 1950s. The Republican presidential nominee has carried the state in every election since 1968.