Charles Ellicott Commentary 2 Chronicles 35:25

"And Jeremiah lamented for Josiah: and all the singing men and singing women spake of Josiah in their lamentations unto this day; and they made them an ordinance in Israel: and, behold, they are written in the lamentations." — 2 Chronicles 35:25 (ASV)

And Jeremiah lamented — that is, wrote a dirge. The special mourning of the land over Josiah is not mentioned in Kings.

The singing men ... women. — The Septuagint has “the ruling men ... women,” reading sârîm ... sârôth, instead of shârîm ... shârôth.

Spoke of Josiah in their lamentations. — In the dirges which they used to sing on certain anniversaries of disaster.

And made them an ordinance. — And they made them (that is, the laments for Josiah) a standing custom to Israel.

They are written in the lamentations. — The dirges alluding to Josiah’s untimely end, and among them Jeremiah’s, were preserved in a Book of Dirges (qînôth), which may have been extant in the chronicler’s day. (Compare the allusions in Jeremiah 22:10; Jeremiah 22:18; Zechariah 12:11.)

This collection, however, was quite different from the canonical book of Lamentations, the subject of which is the ruin of Judah and Jerusalem by the Chaldeans.