MD 623 intersects Glen Cove Road and crosses Peddler Run in the village of Castleton before curving to the west.

The state highway turns north onto Flintville Road, which heads through a forested area.

MD 623 veers northwest and crosses Broad Creek, which is wide at this point from the backwater of the Susquehanna River from Conowingo Dam.

[1][2] Flintville Road continues north as SR 2043 in Peach Bottom Township in the southeast corner of York County.

[8][9] The highway's southern terminus was moved the short distance south to MD 161 in 1978.