Koniuji Island has a land area of 0.37 sq mi (237 acres) and is uninhabited.

[1] The Aleut name is Tanax̂silĝux̂ "the big made island", in reference to putative recent volcanic activity.

The northwest end of the island is a low, flat, rocky point about 200 yards (180 m) long.

There are also large numbers of the Ancient Murrelet and the Whiskered Auklet that nest on Koniuji.

These four species breed on Koniuji Island in numbers that exceed 1% of their total global populations.