Fall Branch is a census-designated place in Washington and Greene counties in the U.S. state of Tennessee. The population was 1,291 at the 2010 census. Some areas in Sullivan also use the Fall Branch ZIP code.Fall Branch 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.