PA 851 is a two-lane undivided road that runs through rural areas in southern York County a short distance to the north of the Maryland border.

The route turns east to remain along Steltz Road and runs a short distance to the north of the Maryland border, passing through the community of Steitz and crossing into Shrewsbury Township.

PA 851 turns northeast away from the state line and continues through a mix of farm fields and woodland with occasional residences.

PA 851 curves east to fully enter New Freedom and turns southeast onto West Main Street, passing a mix of homes and businesses.

PA 851 crosses into the borough of Railroad and becomes South Main Street, quickly turning west and then north as it runs through a mix of woods and residences.

The road continues through wooded areas with some homes before leaving Railroad for Shrewsbury Township and turning northeast through farm fields.

Following this interchange, PA 851 runs past more commercial establishments before narrowing to two lanes and heading southeast, passing to the north of a park and ride lot.

The route passes through the communities of Orwig, Reimold, and Zeigler before it runs through residential areas and heads into the borough of Stewartstown.

Here, PA 851 becomes North Hill Street and heads southeast through industrial and commercial areas, crossing the Stewartstown Railroad.

The route passes homes and some businesses, turning east onto West Pennsylvania Avenue and continuing to an intersection with PA 24 in the center of Stewartstown.

[2][3] The route leaves Stewartstown for Hopewell Township again and becomes Pleasant Valley Road, running through agricultural areas with occasional trees and homes.

PA 851 curves northeast before it turns southeast onto Woolen Mill Road and winds through a mix of farmland and woodland with some homes.

The route becomes West Main Street and runs through farmland with some trees and development, bending southeast as it passes south of Kennard-Dale High School and entering the borough of Fawn Grove.

The truck route heads southeast from PA 851 in the center of the borough of New Freedom along two-lane undivided West Main Street.

PA 851 Truck turns north onto South Main Street and passes homes and a few businesses, crossing the abandoned Stewartstown Railroad.