PA 117 begins at a partial cloverleaf interchange with the US 322/PA 72 freeway in the borough of Cornwall in Lebanon County, heading west as a two-lane undivided road.

The road curves west and southwest again, passing to the north of the community of Mount Gretna Heights.

PA 117 runs near the northwestern border of the borough of Mount Gretna as it passes between wooded residential areas to the southeast and Conewago Lake to the northwest, with the name becoming Mt.

The road enters South Londonderry Township and winds west through more forests, running parallel to the Conewago Creek and eventually the Lebanon Valley Rail Trail.

The road curves northwest and runs through forested areas with some fields, passing to the southwest of a wooded residential neighborhood.

PA 117 turns north and passes near residential subdivisions and some farms before it comes to a junction with US 322 to the east of the community of Campbelltown.

The road passes to the east of the Reigle Field airport and continues through farmland with some development as it enters North Londondery Township.