Washington County is a county located in the U.S. state of Tennessee. As of the 2010 census, the population was 122,979. Its county seat is Jonesborough. The county's largest city and a regional educational, medical and commercial center is Johnson City.
Washington County is part of the Johnson City Metropolitan Statistical Area, which is a component of the Johnson City–Kingsport–Bristol, TN-VA Combined Statistical Area – commonly known as the "Tri-Cities" region.
Washington County, Tennessee, was established by European-American colonists in 1777 as Washington County, North Carolina. It was named for General George Washington while the Revolutionary War was underway. At that time, the county included the entire geographic area that would later became the State of Tennessee, and was also known as the Washington District. From 1784 through 1788, the county was part of the State of Franklin, an early attempt to create a fourteenth state prior to Kentucky and Vermont's admissions into the union. It then became part of the Southwest Territory in 1790, and finally, part of Tennessee after it was admitted to the Union in 1796 as the 16th state.
Jonesborough, the county seat of Washington County, is Tennessee's oldest town. With many buildings restored, it comprises one of the nation's most authentic historic districts of the period 1790 - 1870.
Johnson City, originally known as Johnson's Depot, was a major railway center for the southeastern states, connecting the region for freight transportation and passengers. It was the headquarters for both the standard-gauge Carolina, Clinchfield, and Ohio (Clinchfield Railroad), which required the excavation and blasting of 17 tunnels during its construction; and the narrow-gauge East Tennessee and Western North Carolina Railroad (Tweetsie). Significant restoration is underway, as well as publicizing the railroad heritage of the Johnson's Depot Historic District. Other historic properties are being restored as representative of Johnson City's late nineteenth and early twentieth-century era as a railway center.