It roughly follows a portion of the path of the historic 1799 State Road[2] from "Bald Eagle's Nest" (Milesburg) to Fort Le Boeuf (Waterford, PA), which was laid out and cleared under contract with the Pennsylvania Assembly and opened for travel by 1802.

The State Road was an important thoroughfare during the War of 1812, and was for many years the primary route for mail, goods and travelers between Philadelphia and Erie.

The route passes through a mix of farmland and woodland prior to entering Moshannon State Forest.

It leaves the state forest, then passes through more woodland with some agricultural clearings and local housing, making a few curves.

At this point, PA 504 turns northeast to form a concurrency with US 220 Alternate on Union Street, running past more residences.