Hastings' Dictionary of the Bible -
Telassar
TELASSAR (‘Asshur’s hill or mound’). This city is mentioned with Gozan, Haran, and Rezeph, and is spoken of as a place inhabited by ‘the children of Eden’ ( 2 Kings 19:12 , Isaiah 37:12 ). The Assyrian inscriptions apparently mention two places so called, one being Til-ashshuri , mentioned by Tiglath-pileser iii., which had a renowned temple dedicated to Merodach, and is stated to have been a Babylonian foundation. The other, written Til-ashurri , is referred to by Esarhaddon as having been conquered by him (the people of Mihrânu, he seems to say, called it Pitânu ). It was inhabited by the people of Barnaku or Parnaku a name which Delitzsch points out as similar to the Parnach of Numbers 34:25 . This Till-ashurri is supposed to have lain near the land of Mitanni (Upper Mesopotamia), which would find support if Mihrânu be connected with the Mehru mentioned by Tukulti-Ninib (-Nirig) 1.
T. G. Pinches.
Easton's Bible Dictionary -
Telassar
Or Thelasar, (Isaiah 37:12 ; 2 Kings 19:12 ), a province in the south-east of Assyria, probably in Babylonia. Some have identified it with Tel Afer, a place in Mesopotamia, some 30 miles from Sinjar.