Albert Barnes Commentary Zechariah 12:11

"In that day shall there be a great mourning in Jerusalem, as the mourning of Hadadrimmon in the valley of Megiddon." — Zechariah 12:11 (ASV)

As the mourning of Hadadrimmon in the valley of Megiddon - This was the greatest sorrow that had fallen on Judah. Josiah was the last hope of its declining kingdom. His sons probably already showed their unlikeness to their father, by which they precipitated their country’s fall. In Josiah’s death, the last gleam of the sunset of Judah faded into night.

It is recorded of him that his pious acts, according to what was written in the law of the Lord, were written in his country’s history (2 Chronicles 35:26, 2 Chronicles 35:7); for him the prophet Jeremiah wrote a dirge (2 Chronicles 35:25); all the minstrels of his country spake of him in their dirges (2 Chronicles 35:25). The dirges were made an ordinance (2 Chronicles 35:25) that survived the captivity; to this day (2 Chronicles 35:25), it is said at the close of the Chronicles. Among the gathering sorrows of Israel, this lament over Josiah was written in the national collection of dirges (2 Chronicles 35:25).

“Hadadrimmon,” as being compounded of the name of two Syrian idols, is, in its name, a witness to how Syrian idolatry penetrated into the kingdom when it was detached from the worship of God. It was (Jerome) “a city near Jezreel, now called Maximinianopolis in the plain of Megiddon, in which the righteous king Josiah was wounded by Pharaoh Necho.” This “was 17 miles from Caesarea, 10 from Esdraelon.” Its name still survives in a small village south of Megiddon, and so, on the way back to Jerusalem.