Charles Ellicott Commentary Jeremiah 2:10

"For pass over to the isles of Kittim, and see; and send unto Kedar, and consider diligently; and see if there hath been such a thing." — Jeremiah 2:10 (ASV)

Pass over the isles ... —Chittim is named as, from the prophet’s point of view, the furthest country in the west (Genesis 10:4; Numbers 24:24), Kedar (Genesis 25:13; Psalms 120:5) in the east. The whole earth might be searched without finding a parallel to the guilt of Israel.