Lilius is a lunar impact crater that is located in the rugged southern highlands of the Moon.

The outer rim of Lilius has been worn down and rounded, particularly to the northwest where the inner wall protrudes farther into the interior floor.

The lowest portion of the rim is to the south, adjacent to a crater attached to the southeast part of the outer wall.

The interior floor is relatively flat and featureless, but there is a wide, domed central peak at the midpoint.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Lilius.