Hannan Trace High School was a public high school located on the edge of Mercerville, at the intersection of Hannan Trace and Mercerville roads in Gallia County, Ohio (US).

It replaced Mercerville High School in 1956 and was in turn replaced by River Valley High School in 1992.

HTHS had a Crown City zip code since Mercerville lacks a post office.

In 1996, the Gallia County School District decided to renovate the old Hannan Trace building and turn it into South Gallia High School.

[3] The building served as the home of the Wildcats, and later, the Rebels, until 2009 when a newer building was set up on the western side of Old Hannan Trace Road and the former school was demolished.