Map - Clark County, Nevada (Clark County)

Clark County is located in the U.S. state of Nevada. As of the 2020 census, the population was 2,265,461. Most of the county population resides in the Las Vegas Census County Divisions, which hold 1,771,945 people as of the 2010 Census, across 476 sqmi. It is by far the most populous county in Nevada, and the 11th most populous county in the United States. It covers 7% of the state's land area but holds 74% of the state's population, making Nevada one of the most centralized states in the United States.

Las Vegas, the state's most populous city, has been the county seat since its establishment. The county was formed by the Nevada Legislature by splitting off a portion of Lincoln County on February 5, 1909, and was organized on July 1, 1909. The Las Vegas Valley, a 600 sqmi basin, includes Las Vegas and other major cities and communities such as North Las Vegas, Henderson, and the unincorporated community of Paradise.

Native Americans lived in the Las Vegas Valley beginning over 10,000 years ago. Paiutes moved into the area as early as AD 700. Previously part of the Mexican Territory of Alta California, the Clark County lands were subsequently traversed by American beaver trappers. Word of their journeys inspired the New Mexican merchant Antonio Armijo in 1829 to establish the first route for mule trains and herds of livestock from Nuevo Mexico to Alta California through the area, along the Virgin and Colorado Rivers. Called the Armijo Route of the Old Spanish Trail, the route was later modified into the Main Route by the passing merchants, trappers, drovers, Ute raiders and settlers over the years by moving to a more direct route. In Clark County it was northward away from the Colorado to a series of creeks, waterholes and springs like those at Las Vegas, to which John C. Frémont added Frémont's Cutoff on his return from California to Utah in 1844.

What is now Clark County was acquired by the United States during the Mexican–American War, becoming part of the northwestern corner of New Mexico Territory. In 1847, Jefferson Hunt and other Mormon Battalion members returning to Salt Lake City from Los Angeles pioneered a wagon route through the County that became the Mormon Road. In 1849, this road became known as the "Southern Route", the winter route of the California Trail from Salt Lake City to Los Angeles during the California Gold Rush. By the mid-1850s, the route now known as the Salt Lake Road in California, and the California Road in Utah Territory, was a wagon trade route between the two. In the mid-1850s, Mormons established a settlement at Las Vegas. In the 1860s, Mormon colonies were established along the Virgin and Muddy Rivers.

All of the county was part of Mohave County, Arizona Territory, when that Territory was formed in 1863, before Nevada became a state. In 1865, it became part of Pah-Ute County, Arizona Territory. The part of Pah-Ute County north and west of the Colorado River was assigned to the new State of Nevada in 1866; however, Arizona territory fought the division until 1871. Pah-Ute County became part of Lincoln County and the westernmost part became the southernmost part of Nye County.

Clark County was named for William A. Clark, a Montana copper magnate and Democratic U.S. Senator. Clark was largely responsible for construction of the San Pedro, Los Angeles and Salt Lake Railroad through the area, contributing to the region's early development. Clark County is a major tourist destination, with 150,000 hotel rooms. The Las Vegas Strip, home to most of the hotel-casinos known to many around the world, is not within the City of Las Vegas limits, but in unincorporated Paradise. It is, however, in the Las Vegas Valley.

Clark County is geographically coextensive with the Las Vegas MSA, a metropolitan statistical area designated by the Office of Management and Budget and used by the United States Census Bureau and other agencies for statistical purposes. Over time and influenced by climate change, droughts in Southern Nevada have been increasing in frequency and severity, putting a further strain on Clark County’s and Las Vegas's water security.