Harpalus is a young lunar impact crater that lies on the Mare Frigoris, at the eastern edge of the Sinus Roris. To the southeast at the edge of the mare is the small crater Foucault, and to the northwest on the opposite edge is the walled plain named South.

The rim of Harpalus is sharp-edged with little sign of wear or erosion. The wall is not perfectly circular, and has a few outward notches and protrusions, especially along the eastern half. It is surrounded by an outer rampart of ejecta, most notably towards the north, and is at the center of a small ray system. Due to its rays, Harpalus is mapped as part of the Copernican System.

The inner surface is terraced, and flows down to the floor. The interior wall is the least wide along the northern face, making the floor slightly offset in that direction. Near the midpoint is a system of low central ridges.