PA 340 enters West Caln Township in Chester County and becomes West Kings Highway, passing southeast through woods and fields and reaching an intersection with PA 10 in the community of Compass. At this point, PA 10 turns southeast for a brief concurrency with PA 340 before PA 340 splits to the east. The road runs through wooded areas with some homes and fields, passing through the community of Wagontown. The route curves southeast before running east again and becoming the border between West Caln Township to the north and the city of Coatesville to the south. PA 340 crosses the West Branch Brandywine Creek and runs along the border between West Brandywine Township to the north and Coatesville to the south as it comes to the junction with PA 82 in the community of Siousca.