The Baltimore & Ohio (B&O) played an important role in the creation of West Virginia. It was a major employer in towns such as Harpers Ferry, Martinsburg, Grafton, Parkersburg, Wheeling, and Clarksburg. The railroad's management eventually sided with the North during the Civil War, influencing many people in the northern part of the area that became West Virginia to support statehood in 1863. Once war started, the route of the rail line affected the shape of the new state.

The B&O was chartered in 1827 as Baltimore's answer to the westward construction of New York's Erie Canal and Pennsylvania's canal system. When passenger and freight operations began in May 1830, the B&O was the first common carrier railroad in the country. The B&O proved that steam locomotion was feasible, and by late 1834 the line had been completed to Harpers Ferry.

It was another decade before the B&O was completed to Cumberland (1842) and yet another decade before the line achieved the original objective of the founders—the Ohio River at Wheeling (1852). Several years later an alternate line from Grafton to Parkersburg was completed. The rugged terrain through what is now West Virginia slowed the construction and increased the cost. It was necessary to sell stock subscriptions and bonds in England to finance the railroad. In the first decade of the company's history a substantial portion of its revenue came from passenger service. With the opening of the coal mines in the area around Cumberland and in the mountains west of that city, coal traffic to Baltimore became the major source of revenue.

John W. Garrett was president of the B&O during the Civil War period. John Brown stopped a B&O passenger train and occupied railroad property in his attack on the U.S. arsenal at Harpers Ferry in 1859. Col. Thomas J. "Stonewall" Jackson commanded VMI cadets at Brown's execution, and returned to Jefferson County as commander of Virginia forces at the outset of the Civil War. By the time Jackson withdrew from Harpers Ferry in June 1861, he had systematically looted the railroad. Tools and equipment were transported deep into the Confederacy and six locomotives were moved, part of the way over highways, to the Manassas Gap Railroad. The bridge over the Potomac was destroyed, and railroad equipment and rolling stock from Harpers Ferry to Martinsburg was damaged or destroyed.

The B&O continued to suffer extensive damage during the war. Nonetheless, dedicated employees, many living in West Virginia, reopened the line quickly and allowed the company to operate at a profit. By the time the Civil War ended the B&O was in a position to expand. This began with the construction of large wrought-iron bridges over the Ohio River at Wheeling and Parkersburg.

By a combination of leases and purchases the B&O reached Columbus, Ohio, Lake Erie, and Pittsburgh (from Cumberland) in 1871. Other lines took the B&O into Virginia at Lexington, to Philadelphia, and eventually to Chicago. At the end of the Civil War the B&O had operated 520 miles of railroad, but by 1884 it had expanded to 1,700 miles. Unfortunately, most of this expansion had been financed by borrowed money. Furthermore, the B&O had engaged in a series of rate wars with the Pennsylvania, the New York Central, and the Erie that reduced profits from its operations. Trouble was brewing.

The railroad industry in the 1870s underwent a significant struggle between management and labor. This peaked during the economic depression of the mid- 1870s, when anti-union efforts and wage cuts increased significantly. A series of national strikes began in Martinsburg in 1877, when B&O employees seized control of the railroad. Local police and the state militia could not handle the situation. Federal troops were required to restore order, and the animosity lasted for many years.

Overexpansion and inadequate income were the major problems faced by the B&O in the late 19th century. The quality of maintenance and service began to decline rapidly. So did the traffic, much of it lost to competitors. In 1889, the B&O hauled 31 percent of the nation's Tidewater-bound soft coal; by 1896, it hauled only four percent. The decline in traffic and the depression of the mid-1890s forced the B&O, along with many other railroads, into receivership.

The B&O recovered from receivership rapidly, partly because of the return of prosperity in the late 1890s, and it continued to expand, primarily by purchasing or by entering into operating agreements with other railroads. In West Virginia it added the Monongahela River Railroad (Fairmont to Clarksburg) in 1900, while in 1901 it began the process of acquiring the Ohio River Railroad from Wheeling through Parkersburg and Huntington to Kenova. In the 1920s, operating agreements were developed with the Morgantown & Kingwood Railroad and the Coal & Coke Railway (Elkins to Charleston), essentially completing its routes in West Virginia. All of these railroads were eventually incorporated into the B&O.

After a short period of control by the Pennsylvania Railroad in the first decade of the 20th century, Daniel Willard became president of the B&O in 1910, a position he would hold until 1941. Willard carried out a major modernization of the system which made the B&O one of the premier American railroads. In the 1920s, it averaged revenues of about $225 million a year with dividends up to six percent.

Then came the Great Depression, hitting the B&O harder than most railroads. Barely surviving receivership, the railroad recovered briefly during World War II and into the early 1950s, but the decline of coal mining along its lines and increasing competition from other railroads and highways placed the company in a weak financial position by 1960. Faced with mounting debt, in 1962 the B&O accepted merger overtures from the Chesapeake & Ohio while rejecting those from the New York Central. The absorption of the oldest common carrier proceeded slowly and was not finalized until 1973. The Chessie System was created that year, and today the B&O is part of the vast CSX transportation system.