From BiblePortal Wikipedia

Fausset's Bible Dictionary [1]

A city in the valley of Megiddo, or plain of Jezreel or Esdraelon; named from Hadad the Syrian sun god and Rimmon, another Syrian idol. (See Rimmon .) The scene of the national lamentation for Josiah's death in the battle fought here with Pharaoh Necho ( 2 Kings 23:29;  2 Chronicles 35:23). Jerome calls the city Maximianopolis, from the emperor Maximian; not far from Jezreel.

People's Dictionary of the Bible [2]

Hadad-rimmon ( Hâ'Dad-Rĭm'Mon ). A place probably named from two Syrian idols, Hadad, the sun-god, and Rimmon. It was in the valley of Megiddo,  Zechariah 12:11, and the scene of a great lamentation over the death of Josiah.  2 Kings 23:29;  2 Chronicles 35:20-25.

Smith's Bible Dictionary [3]

Ha'dad-rim'mon. Hadadrimmon is, according to the ordinary interpretation of  Zechariah 12:11, a place in the valley of Megiddo, (a part of the plain of Esdraelon, six miles from Mount Carmel and eleven from Nazareth), where a national lamentation was held for the death of King Josiah. It was named after two Syrian idols.

Easton's Bible Dictionary [4]

 Zechariah 12:11 2 Chronicles 35:22-25

Holman Bible Dictionary [5]

 Zechariah 12:11

Cyclopedia of Biblical, Theological and Ecclesiastical Literature [6]

(Heb. Hadad'-Rimmon', רַמּוֹן הֲדִד the names of two Syrian idols; Sept. Κοπετάς Ροὼνος ,Vulg. Adadremmon), the name of a place in the valley of Megiddo, alluded to in  Zechariah 12:11 as a type of the future penitence of the Jews; probably by a proverbial expression from the lamentation for Josiah, who was mortally wounded not far from this spot ( 2 Chronicles 35:22-25). (There is a treatise by Wichmanshausen. De Planctu Hadadr. in the Nov. Thes. Theol. Phil. 1, 1101; exegetical remarks on the same text have also been written in Dutch by Vermast [ Gonda, 1792, 1794], in German by Mauritii [Rost. 1764. 1772], and in Latin by Froriep [Erf. 1776].) According to Jerome ( Comment. On Zechariah 1 . c. and Hosea 1 ), it was afterwards called Maximliunoopolis (see Reland. Palcest. p. 891), which, according to the Jerus. Itin., lay 17 Rom. miles from AEesatea, and 10 from Esdraelon; being situated, according to Dr. Robinson (new ed. of Researches, 3, 118), a little south of Megiddo (now Lejjun) (see Bibliotheca Sacra, 1844, p. 220). The name has been thought to be derived from the worship of the idol Hadad-rimmon (Hitzig on Isaiah 17, 9; Movers, Phin. p. 297); but, according to the Targum of Jonathan (followed by Jarchi), it is an ellipsis for Hadad, son of Tab-rimmon, the alleged opponent of Ahab at Ramoth-Gilead. As it contains the names of two principal Syrian deities, it may have been an old Syrian stronghold, and hence Josiah may here have made his last stand in defense of the plain of Esdraeloa. Such a site, therefore, does not ill agree with the position of the modern Runlaneh, a village "at the foot of the Megiddo hills, in a notch or valley about 1 hour S. of tell Metzellim" (Van de Velde, Memoir, p. 333; comp. Narrative, 1, 355; De Saulcy, Dead Sea, 2, 311). Schwarz's attempt (Palest. p. 159) to identify Hadad-Rimmon with Gath-Rimmon of  Joshua 21:25, as the Kefar Uthni of the Talmud ''(G '''''Ö''''' Tting, fol. 76, a), and a present Kafer Guth, said by him to be located about 24 miles from Lejjun, beyond Sepphoris, is without foundation.