The Tennessee General Assembly established Franklin County in 1807, following the extinction of Cherokee claims west of the Cumberland Plateau between the Duck and Tennessee Rivers. Mountain lands were added after Native American claims ended in 1819. Franklin County was named for Benjamin Franklin, whose name had already been borrowed in 1784 for East Tennessee's abortive state. The county seat was named for General James Winchester. The county’s population totaled 39,270 in 2000.
Whites and blacks had visited the area, notably during the 1794 Nickajack expedition, and speculators had claimed large tracts still in Native American hands, but creation of the county opened the way for settlers, mostly from East Tennessee, North Carolina, and Virginia. Among the first settlers were William Russell on Boiling Fork near Cowan and Jesse Bean in the southwest part of the county. Russell's house served as the courthouse until Winchester was laid out in 1810. Davy Crockett made his home near Bean between 1813 and 1817. By the time of the War of 1812, Franklin County had enough settlers to answer Andrew Jackson's call for volunteers to oppose the Creek uprising in Alabama.
Franklin County was primarily a farming region. Cotton was floated down the Elk River to New Orleans early in the county's history, but as in much of the mid-state area, land was better for corn, wheat, and livestock. With the advent of improved roads and turnpikes, wagon trains moved produce to Nashville and returned with supplies; access to Huntsville in North Alabama was also easy.
In 1854 Vernon K. Stephenson transformed the county when he built his Nashville and Chattanooga Railroad through Decherd, tunneling the Cumberland Plateau between Cowan and Sherwood and dipping into Alabama to join the Western and Atlantic into Georgia and the East Tennessee and Georgia to the northeast. Within four years, the Sewanee Mining Company built a line up the mountain from Cowan, and another was completed from Decherd to Fayetteville and later extended to Huntsville and Lewisburg.
Franklin County was a Confederate seedbed. Franklin County native Isham G. Harris, a secessionist, was elected governor in 1857, 1859, and 1861. Peter Turney, a future governor, recruited a regiment that mustered into the Confederate service before Tennessee held its plebiscite on secession. Turney circulated petitions to have Franklin County secede from Tennessee if the state did not leave the Union. In the statewide vote, Franklin County reported unanimous support for secession despite pockets of resistance.
Federal troops arrived in Franklin County in 1862, although Confederates reestablished control. After the Confederate defeat at Murfreesboro in January 1863, the Southern army retreated to Tullahoma, filling Franklin County with sick and wounded until July 1863, when it abandoned Middle Tennessee for Chattanooga, exiting along local roads. Thereafter Franklin County remained under Federal control, with the Nashville and Chattanooga Railroad serving as the primary supply line for operation against Chattanooga and Atlanta.
In the postwar years, newly freed African Americans created new communities and institutions such as the First Baptist (Missionary Baptist) Church and the St. John AME Church in Winchester. Most residents of Franklin County remained farmers, but agriculture made a slow recovery. In addition to farming, the county profited from extractive industries that exploited iron, coal, timber, and stone. The Nashville, Chattanooga and St. Louis Railroad became the preferred passenger route between midwestern cities and economic development in Florida, spawning hotels and restaurants along its route. Resorts flourished at Winchester Springs and along the Cumberland Plateau. Franklin County also became known for its educational institutions, notably Mary Sharp College in Winchester, which had pioneered in antebellum collegiate education for women, and the University of the South at Sewanee. Other colleges included Winchester Normal and Terrill in Decherd.
In the 1870s Franklin County experienced a period of agrarian unrest which led to the organization of granges, or units of the Patrons of Husbandry. The eastern side of the county experienced labor unrest when state prisoners displaced local miners. Winchester became embroiled in the temperance controversy and surrendered its charter in order to close its saloons under the Four Mile Law, which forbade alcohol sales outside incorporated towns.
Agriculture eventually recovered, especially on farms established by Swiss-German immigrants around Belvidere; their round barns gave the area a European appearance. Early in the twentieth century, farmers began planting large fields of crimson clover for seed, giving a theme to a later celebration and ball. Nevertheless, agriculture shaped the county's twentieth-century character less than the World War II development of Camp Forrest as an army training facility along the county's northern border. The installation brought thousands of military families to the area. In 1952 the deserted camp became home to Arnold Engineering Development Center (AEDC) for testing advanced aerospace technology for the Air Force.
AEDC's need for water led to the damming of Elk River to create Woods Reservoir. The Tennessee Valley Authority built Tims Ford Dam, producing lakefront properties, weekend boating, and a state park. Economically, the county moved from a dependence on extractive industries through a period characterized by small textile and garment mills to its present industrial base of automotive parts and assembly plants. Although agricultural acreage has declined, many farms remain profitable, and the expansion of nurseries east of Winchester has suggested new uses for rich agricultural lands.