SR 320 is located entirely within the northwestern corner of
Preble County. The route begins at its intersection with US 35 south of where the U.S. route converges with I-70 at the Interstate's westernmost interchange in Ohio in
Jackson Township. SR 320 travels to the west-northwest through rural farmland prior to bending to the west into the hamlet of New Westville, where the highway encounters a primarily residential area. At a four-way stop intersection there, SR 320 turns to the north, taking over for New Westville Road while CR 335 is the roadway that departs the intersection to the west. SR 320 now turns to the north-northwest, passing amidst a number of houses prior to crossing over the I-70/US 35
concurrency. To the north of the grade separation, SR 320 travels due north, and is bounded by homes and a large commercial facility on the west side, and farmland on the east side, with some batches of trees appearing along the way. It intersects US 40, then proceeds into
Jefferson Township. A combination of woods and homes appear along the west side of the highway at this point, with more farmland abutting it to the east. After a short reverse curve that takes the highway to the northeast and then back to the north, SR 320 encounters forested land on both sides. Upon emerging from the wooded terrain, the highway enters New Paris. As it follows Washington Street northerly through the
village, SR 320 passes amidst a blend of commercial businesses and residences leading up to its endpoint in downtown New Paris at a signalized intersection where it meets SR 121. This state highway is not included within the
National Highway System. ==History==