PA 305 begins at an intersection with US 22 in Porter Township, Huntingdon County, heading north on two-lane undivided Bridge Street. The road heads through areas of homes with some farm fields, crossing the Frankstown Branch Juniata River into the borough of Alexandria. Here, the route turns east-southeast onto Main Street, passing through more residential areas. PA 305 heads back into Porter Township and turns northeast onto Juniata Valley Pike, entering agricultural areas with occasional homes. The route crosses the Little Juniata River into Logan Township and comes to a bridge over Norfolk Southern's Pittsburgh Line, turning east onto West Diamond Street. The road runs through more agricultural areas before it enters the borough of Petersburg and becomes Diamond Street, passing homes. PA 305 turns north onto King Street and runs past more residences, turning northeast onto Shavers Creek Road and entering Logan Township again. At this point, the route heads through farmland with some homes and patches of woods, heading through the community of Ribot. The road continues into West Township and passes through more rural areas, running through Cottage and Neffs Mills. In the residential community of Mooresville, PA 305 turns southeast onto Greenwood Road and winds through open farmland with some homes, crossing into Barree Township. In this area, the route heads through wooded areas with some farm fields. The road passes through Manor Hill and heads east through farmland before passing through more woodland and curving northeast at Saulsburg. PA 305 continues into a mix of farms and woods with some residences as it heads into Jackson Township, where it turns southeast into open agricultural areas, curving east and coming to an intersection with PA 26 in Ennisville. Here, PA 26 turns east to form a concurrency with PA 305, crossing the Standing Stone Creek and running through more rural areas with some homes. PA 305 splits from PA 26 in McAlevys Fort by turning to the southeast, remaining along Greenwood Road and passing through more farmland. The road turns to the northeast before heading east into Rothrock State Forest, where it begins to ascend Stone Mountain. The route heads to the east-northeast and passes through Greenwood FurnaceState Park and the community of Greenwood Furnace before passing through more of the state forest, turning to the south and before curving to the southwest. At the top of the mountain, PA 305 crosses into Union Township in Mifflin County and leaves the boundaries of Rothrock State Forest. The route begins to descend the forested mountain, curving to the east. At the base of Stone Mountain, the road turns to the southeast and heads into the Kishacoquillas Valley, an agricultural valley which is home to an Amish community. Here, the route runs through farmland with some residences. PA 305 continues southeast to its eastern terminus at an intersection with PA 655 near the community of Belleville.
