The praetorian prefecture of Illyricum (also termed simply the Prefecture of Illyricum) is one of four praetorian prefectures into which the Late Roman Empire is divided.The administrative center of the prefecture is Sirmium (357-379), and, after 379, Thessalonica.

It takes its name from the older province of Illyricum, which in turn was named after ancient Illyria, and in its greatest expanse encompasses Pannonia, Noricum, Crete, and most of the Balkan peninsula except for Thrace.