O'Day is a prominent lunar impact crater that is located on the far side of the Moon. It is intruding into the northwestern edge of Mare Ingenii, and the rim is lower on that side. To the northwest is the crater pair of Holetschek and Sierpinski . Southwest of O'Day lies the Seidel crater .

The crater rim of O'Day remains sharp-edged, and the inner wall is terraced, escpecially in the northwest half away from the mare. A small crater lies across the southern rim, and a tiny craterlet is located in the low inner rim between the crater and the mare. The floor is rough and irregular, with a double-peak at the mid-point.

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 O'Day crater.