The western terminus of the route is at the eastern border of York, where the road continues west as East Prospect Street towards PA 74.

The route ran east to Craley before it continued southeast to the York Furnace area, where it crossed the Susquehanna River.

A short distance after beginning, PA 124 makes a turn southeast to become Mount Rose Avenue, leaving York for Spring Garden Township.

The route bends east and passes between and industrial areas to the north and a cemetery to the south before it runs past more residences.

PA 124 crosses the Mill Creek into Springettsbury Township and widens to a four-lane divided highway, reaching an interchange with I-83.

Past this interchange, the route passes businesses before becoming a four-lane undivided road and heading through suburban residential areas.

The road heads into less dense areas of homes with some trees and fields, curving southeast before turning back to the east.

The route curves northeast and runs through more rural land, bending east and crossing the Kreutz Creek into Lower Windsor Township.

The road runs past more residences and a few businesses before it leaves East Prospect for Lower Windsor Township again.

[7][8] The entire length of PA 124 was paved in the 1930s except for a short stretch to the south of Woodbine, with a section of road to the east of York widened into a multilane highway.