Illyricum

a country to the north-west of Macedonia, on the eastern shores of the Adriatic, now almost wholly comprehended in Dalmatia, a name formerly given to the southern part of Illyricum (2Tim 4:10 ). It was traversed by Paul in his third missionary journey (Rom 15:19). It was the farthest district he had reached in preaching the gospel of Christ. This reference to Illyricum is in harmony with (Acts 20:2), inasmuch as the apostle's journey over the parts of Macedonia would bring him to the borders of Illyricum.

EBD - Easton's Bible Dictionary