Pennsylvania Route 128 (PA 128) is an 15-mile (24 km) long state highway located in Armstrong county in Pennsylvania. The southern terminus is at PA 356 in Freeport. The northern terminus is at PA 66 in Ford City.

PA 128 begins at an intersection with PA 356 in Freeport, where it becomes a one-way pair. Northbound PA 128 heads south from PA 356 on two-lane undivided 2nd Street past homes. The route turns east onto Market Street and heads into the commercial downtown area, where PA 128 turns north onto 5th Street. Southbound PA 128 heads southeast from PA 356 on two-lane undivided Buffalo Street, passing homes before turning south onto 5th Street and running past businesses. At the intersection of 5th Street and High Street, both directions of PA 128 meet and head east on two-lane undivided High Street, lined with residences. The road turns northeast and crosses into South Buffalo Township, entering wooded areas as it becomes Freeport Road. PA 128 continues north and skirts the border between Freeport to the west and South Buffalo Township to the east as a three-lane road with two northbound lanes and one southbound lane. The road passes through woodland with some homes within South Buffalo Township, running through the community of Dock Hollow. Farther north, the route enters a mix of farmland, woods, and residences as it heads more to the northeast and passes through Kerr. At this point, PA 128 curves to the north and continues to an interchange with the PA 28 freeway.

A short distance past this interchange, the route reaches Slate Lick and turns east onto Cadogan Slate Lick Road, passing through more rural areas with some residences. The road crosses into North Buffalo Township and passes under the PA 28 freeway without an interchange. PA 128 continues east before turning south into forested areas and entering Cadogan Township. The route becomes Main Street and heads into the community of Cadogan, passing homes. PA 128 turns northeast onto Prospect Avenue and passes more residences before crossing back into North Buffalo Township and becoming Ford City Road. The road heads through woods before coming into areas of fields and homes. The route turns southeast and comes to a bridge over the Buffalo & Pittsburgh Railroad and the Allegheny River, entering Manor Township. PA 128 curves northeast and heads into Ford City, becoming 5th Avenue as it passes numerous homes. The road runs through the commercial downtown of Ford City before continuing past more residences and businesses. PA 128 crosses back into Manor Township and comes to its northern terminus at an intersection with PA 66.

The entire route is in Armstrong County.