Pennsylvania Route 921 (PA 921) is a 10-mile (16 km) long state highway located in York county in Pennsylvania. The western terminus is at PA 74 in Dover. The eastern terminus is at PA 24 in Mount Wolf.

PA 921 begins at an intersection with PA 74 in Dover, heading northeast on two-lane undivided Canal Road. The road passes a mix of homes and businesses before turning east and becoming the border between Dover to the north and Dover Township to the south, passing residential subdivisions. The route fully enters Dover Township as it turns northeast into wooded areas of homes before passing a mix of farmland and residences. Upon crossing Bull Road, PA 921 heads into Conewago Township and passes more agricultural areas with some patches of woods and housing. The road intersects PA 295 in the community of Zions View, where it makes a turn to the east and crosses the Little Conewago Creek, becoming the border between East Manchester Township to the north and Manchester Township to the south as it passes under I-83. Immediately after, PA 921 turns northeast into East Manchester Township and passes farm fields.

The road turns southeast onto Zions View Road and passes more areas of agriculture before entering Manchester and becoming Musser Street. Here, PA 921 passes homes before it turns north to form a concurrency with PA 181 on Main Street. The two routes pass residences and businesses in the center of town before PA 921 splits from PA 181 by heading east on Maple Street. The road passes more residences and continues into Mount Wolf. Here, PA 921 crosses a Norfolk Southern railroad line and turns southeast to reach its eastern terminus at the northern terminus of PA 24.

The entire route is in York County.