Jefferson City is a city in Jefferson County, Tennessee, United States. It is part of the Morristown Metropolitan Statistical Area. As of the 2020 c…Jefferson City is a city in Jefferson County, Tennessee, United States. It is part of the Morristown Metropolitan Statistical Area. As of the 2020 census the population was 8,419. Heading southwest along the Holston River from Virginia, Adam and Elizabeth Peck arrived on the banks of Mossy Creek in 1788, soon settling the area with a fort, a house of worship, and a gristmill. It is suggested that the original name of the city, Mossy Creek, originated due to the first settlers' description of the 'vivid' green moss developed around a creek near the settlement. By 1797, Mossy Creek had around 75 to 100 families with a four-mile-radius of the city.