Business Loop I-75 - Piqua

County Road 25A continues north from Exit 78, where the Troy business loop ended as the Piqua business loop. The 5.3 mile route takes Main Street through the city. SR 66 begins at U.S. 36 (Water Street) in Downtown and lines Main Street north to Riverside Drive. Upon crossing the Great Miami River, N Main Street becomes Miami County Road 25A again as it arcs east back to I-75 at Exit 83.

The route is no longer posted from the I-75 mainline or along Main Street in Piqua.