From Halopedia, the Halo wiki
The Kerrec Irruption is a "natal anomaly" in the Milky Way. Little is known of the location, though it is described as a "prison marked by crystallized shard of time" to "tempt the unwary", alongside the Etran Harborage and IX-KA anomaly.
The map found on pages 12-13 of Halo: Warfleet – An Illustrated Guide to the Spacecraft of Halo places the Kerrec Irruption in the Perseus Arm of the Milky Way. Given the general inaccuracies presented in this map, the canonicity of this stated location is unclear.