Cyrillus is a lunar impact crater located on the northwest edge of Mare Nectaris. Intruding into the northeast rim is the equally-large, and younger Theophilus crater. To the south is another prominent crater named Catharina. Together these three craters form a prominent trio in the southeast quadrant of the moon. To the southeast of Cyrillus is the heavily-worn remains of the crater Cyrillus F. To the northwest is Ibn Rushd crater.

The rim of Cyrillus crater has been eroded, although it remains intact except where overlaid by Theophilus crater. The floor is rough and irregular, with three distinct central peaks offset slightly to the northeast. The western peak is designated Alpha (α), the eastern Eta (η), and the southern peak Delta (δ) Cyrillus. A pair of curved clefts lie to the southwest and west of the central peaks. The small crater 'Cyrillus A' lies on the inner wall of the east-southeast rim.

Satellite craters

By convention these features are identified on Lunar maps by placing the letter on the side of the crater mid-point that is closest to Cyrillus crater.

The following craters have been renamed by the IAU.

• Cyrillus B — See Ibn Rushd crater.