Grant County is located at the western end of the Eastern Panhandle of West Virginia. It was created February 14, 1866, soon after the Civil War, and named for Gen. Ulysses S. Grant, who later became the nation's 18th president. Grant County was carved from the territory of Hardy County. Laurelton, near the center of the new county, was briefly the county seat. After that, Maysville was county seat, until 1872, when a vote of the citizens brought the seat of government permanently to Petersburg.

The picturesque landscape ranges from the Allegheny Front and Dolly Sods in the north to the broad beautiful valley of the South Branch of the Potomac River. The historic Fairfax Stone marks a corner of Grant County, at the headwaters of the Potomac River. Early planters, many of them slaveholders, gained title to the fertile bottomland along the river valleys, especially the South Branch Valley in present Hardy County, but the hill farmers, often Unionist in sentiment during the Civil War, composed a major portion of the population. This fostered the creation of the new county in 1866.

Natural resources have long been the key to the economy of Grant County. Farming has been a basic occupation, especially livestock and poultry production. Coal mining in the Alleghenies and timber industries throughout the county brought prosperity at various times in the region's history. Huge logging projects in the late 19th and early 20th centuries provided much lumber for urban expansion along the eastern seaboard. Another key commodity of the forest was the bark of the chestnut oak, which drew the leather tanning industry to the area. Tanneries sprang up throughout the region, with especially large plants in Petersburg and Gormania. The Hoffman and Sons Tannery of Gormania was reputed to be the largest tannery in the world. Tanneries provided jobs in the plants, and much-needed seasonal income to the farmers who peeled bark from trees in their woodlands. Today forest industries remain important. Allegheny Wood Products is a leader in the industry, with a host of independent operators involved in timber production.

A key boost to the economy was the construction in 1965-66 of a huge minemouth generating plant by Virginia Electric Power near Mount Storm. It continues to provide power to Vepco's regional network under the management of Dominion Resources. Other key industries include Adell Polymers, which specializes in extruded plastics. Prior to its closing several years ago, Allied Egry, a division of SCM Corporation, supported a large workforce engaged in the printing of business forms. Grant County Mulch is a large processor of forest byproducts for the Mid-Atlantic market.

Petersburg has become a regional health provider with the expansion of Grant Memorial Hospital. Recently, a Veterans Administration clinic became part of the complex. The Grant Rehabilitation & Care Center has also grown to serve the increasing number of elderly persons in the area.

Education has been a key to county development. Beginning with a large number of one-room schools to serve the widespread population of the county, the present system includes elementary schools at Maysville and Petersburg; a high school at Petersburg; and a combined primary and secondary school complex at Mount Storm. South Branch Career & Technical Center at Petersburg has served students and adults from Grant, Hardy, and Pendleton counties for many years.

The county's history includes famous visitors such as George Washington, whose diaries recount early visits to the area while surveying for Lord Fairfax; Confederate Gen. Jubal A. Early, Union Gen. John C. Fremont, and Col. (later Gen.) James A. Mulligan were there during the Civil War. Mulligan, commander of the 23rd Illinois Regiment, was largely responsible for the construction of the fortifications overlooking Petersburg. The site, known locally as Fort Mulligan, is one of the best preserved fortifications in West Virginia. Recently, with the cooperation of local units of Sons of Confederate Veterans and Sons of Union Veterans, the Civil War Preservation Trust purchased the historic site for local management, making it a key attraction for visitors to the area. The group has also secured an easement for the development and publicizing of the site of the Battle of Greenland Gap, near Scherr.

Transportation has always been an issue in the opening and the development of the area. The earliest settlers followed streams, animal paths, and Indian trails. Nearly a century passed before the first great road project, the construction of the Northwestern Turnpike (modern U.S. 50), opened the northern section of the county on its way to the Ohio River. Road building continues to the present, with the long-anticipated Corridor H four-lane highway under construction. The railroad came to Grant County in 1910, as the Hampshire Southern Railway completed construction to Petersburg. Today the local railroad is operated by the State Rail Authority as the South Branch Valley Railroad.

Petersburg also boasts the area's best airport, with a paved runway capable of accommodating corporate jets. The Petersburg Wave, a powerful updraft which is strongest in early spring, attracts glider pilots from all over the country each March.

No brief history of the land and people of Grant County would be complete without acknowledging both the beauty and the destructive power of the South Branch. Major floods brought devastation in 1924, 1936, and 1949. Worst of all was the great flood of 1985, which left 13 people dead in Grant County and much property damage. In normal times, the South Branch is a peaceful neighbor and an important recreation resource. The river, which makes its way into Grant County through rugged Smoke Hole canyon, is joined by the North Fork, a major tributary, just above Petersburg.

The population of Grant County in 2012 was an estimated 11,816, having risen steadily from 8,607 in 1970. The population was down slightly to 10,976 in 2020. The county is 480.3 square miles in area. In 2023, Grant County's largest employers were Grant Memorial Hospital, the county school system, Virginia Electric and Power, Grant Rehabilitation & Care Center, and A.L.L. Construction.