Pocahontas County is the third largest county in West Virginia, with 941.6 square miles, but among the least populous, with a 2020 population of 7,869, a nearly 10 percent decline from the 2010 census and its lowest total since 1890. Elevations range from slightly under 2,000 feet to several points above 4,800 feet. Located mostly within the upper Greenbrier Valley, Pocahontas County is underlain by sandstone, shale, and limestone.

Eight rivers have their headwaters in the county. The Cherry, Cranberry, Elk, Gauley, Greenbrier, Tygart Valley, Williams rivers, and Shavers Fork of the Cheat River all originate in Pocahontas County. The river headwaters are protected by the Mongahela National Forest, ensuring downstream water quality.

At the time of first European movement into the Greenbrier Valley, Indians did not have permanent settlements in the area. Generally accepted as the first settlers of European descent are Jacob Marlin and Stephen Sewell, who located at present Marlinton about 1749 and remained until at least 1751. Settlement was under way by the early 1750s, but Indian attacks during the French and Indian War drove most settlers out of the valley. Settlement resumed in 1761, but attacks continued through the Revolutionary period and until at least the early 1790s.

The act creating Pocahontas County was passed by the Virginia General Assembly on December 21, 1821. The land came mainly from Bath County, plus small parts of Randolph and Pendleton. Huntersville was selected as the county seat. The 1830 census counted 2,542 residents.

In the years before the Civil War, road improvements helped to reduce isolation. Turnpikes from Warm Springs, between Lewisburg and Huttonsville, and from Staunton to Parkersburg made travel easier. In 1854-56, a bridge was constructed across the river at Marlins Bottom.

There are references to schools as early as the 1790s. A major improvement came in 1842 when the General Assembly chartered three academies for the preparation of students for the University of Virginia, at Green Bank, Hillsboro, and Huntersville. Today there are five schools in Pocahontas County.

The first church is believed to have been the White Pole Meeting House, built before the Revolutionary War. It continues today as the Wesley Chapel United Methodist Church in Hillsboro. A Presbyterian congregation was organized in the Hillsboro area between 1783 and 1788. Today the original Methodists, Presbyterians, and Episcopalians have been joined by adherents to many creeds and denominations.

Excellent grazing lands in the Little Levels and other areas supported the beginnings of the livestock industry that is still important today. Slaves were present from the earliest years but not in extensive numbers, as farms were not large.

Pocahontas County voters supported Virginia's secession from the Union by a 360 to 13 vote, but Pocahontas sent sons to both armies in the Civil War. In the late summer of 1861, the county suddenly became part of the front line. Local activity that fall and winter included a brief visit by Robert E. Lee; battles at Cheat Mountain, Bartow, and Top of Allegheny; and a miserable winter for the men of both armies stationed at the highest camps in elevation used during the war. Movements by a Union force in late 1863 resulted in the last significant Civil War battle in West Virginia, at Droop Mountain on November 6. The federal victory helped to assure Northern control and thus the survival of the new state.

The completion of the Chesapeake & Ohio (C&O) Railway into neighboring Greenbrier County in 1869 brought a railroad near, and a timber boom ensued. By the late 1870s, Pocahontas County logs were being floated to Ronceverte. Until 1908, the drives were an annual event on the Greenbrier River. The Williams River and, less successfully, the Shavers Fork of Cheat were also used to move logs. Pocahontas County sawmill operators also floated rafts of lumber to the railroad.

In the early 1880s, investors began to buy up Pocahontas land and timber. They included John T. McGraw and U.S. Senators Johnson N. Camden and Henry Gassaway Davis. These men and others worked to bring a railroad into the upper Greenbrier Valley. McGraw purchased the land at Marlinton in 1891, and on December 8, 1891, the voters approved Marlinton as the new county seat. The first newspaper in the county, the Pocahontas Times, was established in 1883.

The Greenbrier Division of the C&O was completed to Marlinton and Cass in late 1900, to Durbin in 1902, and on to Winterburn in 1905. In 1903, the Coal & Coke Railway (later part of the Western Maryland Railway) was completed from Elkins to Durbin, connecting with the C&O. Numerous sawmills were quickly put in operation along the new railroad lines, as well as tanneries at Frank and Marlinton. With the need of the lumber companies for farm products and the easier access to market provided by the railroads, agricultural output grew. There were 15,002 residents in 1920, the most ever recorded.

By the late 1920s, virtually the entire county had been timbered. Much land was damaged in the 1930s by severe forest fires that followed the logging. The Monongahela National Forest was created in 1920, and the first land for the forest in Pocahontas County was acquired in 1923. The Depression brought the Civilian Conservation Corps, which located 10 camps within the county. In addition to reforestation and fire control, the CCC did the original development of Droop Mountain Battlefield and Watoga state parks, Seneca State Forest, and Edray Fish Hatchery.

Since World War II the tanneries and the largest lumber operation (Cass) have closed, both railroad lines into the county have been abandoned, and farming has declined. On balance, several new timber-related operations have opened, and the county remains a leader in cattle and sheep production. Tourism has grown from a minor part of the county's economy, based on hunting and fishing, into a major industry. After the Cass mill closed in 1960, the state acquired the remaining segment of logging railroad and created the Cass Scenic Railroad State Park. Calvin Price State Forest, Bear Town State Park, Handley Wildlife Management Area, and the Greenbrier River Trail are also state-owned recreational facilities.

The Snowshoe ski area opened on Cheat Mountain in 1974. An adjoining ski area, Silver Creek, opened in 1983. Snowshoe Mountain Resort (now including Silver Creek) has become the largest ski area in the southeastern United States and the county's largest employer.

In 1955, the Deer Creek Valley near Green Bank was selected for the new National Radio Astronomy Observatory, with the first telescope completed in 1959. The newest telescope at Green Bank is the largest fully steerable radio telescope in the world. The observatory was a major factor for the location of the National Youth Science Camp in the county in 1963.

Post Civil War economic growth brought a broadening of the population mixture. Railroad construction and the lumber industry brought in workers of Italian, Austrian, German, and other national origin (few remained once the jobs were gone, however) as well as additional blacks. A group of Dutch immigrants arrived in 1847, and descendants of these settlers include the author Pearl S. Buck. English immigrants settled in the Linwood-Mingo area, beginning in 1883. In the 1960s and 1970s, a number of homesteaders belonging to the back-to-the-land movement came to the county. The Green Bank Observatory and Snowshoe have brought other new residents.

Floods have been a major factor in the county's recent history. There were significant floods in 1908, 1913, 1933, 1936, and 1967. The flood of November 4-5, 1985, was the largest of the past century, and on January 19, 1996, a flood almost as big hit the county. Flood control has been a dominant concern of the county's citizens in recent years.

Since 1967, the Pioneer Days festival in Marlinton has celebrated Appalachian traditions.

In 2023, Pocahontas County's largest employers were Snowshoe Mountain, the county school system, Pocahontas Memorial Hospital, Associated Universities, and Inter-State Hardwoods