Mountain City is a town in Johnson County, Tennessee, United States. The population was 2,383 at the 2000 census. It is the northeasternmost county seat in Tennessee; Mountain City is the county seat of Johnson County. According to the United States Census Bureau, the town has a total area of 3.3 square miles (8.6 km²), all land. At just over 2,400 feet (730 m), Mountain City is situated in one of the highest valleys in the state of Tennessee.
Doe Mountain rises to the southwest, Forge Mountain rises to the east, and a series of rugged hills (part of the Iron Mountains) dominate the landscape to the north. The Tennessee-North Carolina border runs opposite Forge Mountain approximately 5 miles (8.0 km) east of Mountain City, and the Tennessee-Virginia border passes about 10 miles (16 km) to the north. U.S. Route 421 (Shady Street) connects Mountain City with Bristol, Tennessee to the northwest and Wilkesboro, North Carolina to the southeast. Tennessee State Route 67 (Main Street), which intersects US-421 near the center of town, connects Mountain City with Elizabethton via a winding route along the shores of Watauga Lake. Tennessee State Route 91 connects Mountain City to Damascus, Virginia (the road becomes Virginia State Route 91 at the state line).