Illeginni is located approximately 34 kilometres (21 mi) directly south of Roi-Namur Island, the northernmost part in the atoll, and 49 kilometres (30 mi) to the northwest of Kwajalein, the largest island and southernmost part of the atoll.

Meck Island was the main base in the test system, while Illeginni was a model of the distributed launch sites.

As Nike-X was modified to become Safeguard, Illeginni's site was changed (before construction) to hold four Sprint and four LIM-49 Spartan launchers.

A number of automated tracking cameras were installed as part of the Safeguard program, and one of these remains in use today to support overall operations of the Ronald Reagan Ballistic Missile Defense Test Site.

[2] A harbor has been dredged in the northern side of the eastern end of the island, where it is its widest.