2 Answers

Jazer (or Jaazer) was a city east of the Jordan River, in or near Gilead, and inhabited by the Amorites. It was taken by a special expedition sent by Moses to conquer it. From theSeptuagint, it appears that Jazer was on the border of Ammon. As an important city it gave its name to the whole of the surrounding territory.Even a "sea of Jazer" is mentioned in Jer. xlviii. 32.

Jazer is stated to have been a fertile land fit for the raising of cattle and a place having many vineyards. It was occupied by the children of Gad, by which tribe it was allotted to the Merarite Levites. In the time of David it seems to have been occupied by the Hebronites, who were descendants of Kohath.^[ It was chosen as one of the stations by David's officers who were sent to number the children of Israel.

According to Josephus, Jazer was captured and burned by Judas Maccabeus. The site of Jazer was defined by Eusebius and Jerome as being 8 or 10 Roman miles west ofPhiladelphia, and 15 miles north of Heshbon, and as the source of a large river falling into the Jordan. It is identified by some scholars with the modern Khurbat ?ar on the road from `Iraq al Amir to Al-Salt; but this identification has been rejected by Cheyne.

 http://en.wikipedia.org/wiki/Jazer

This is what I've learned.

http://bibleatlas.org/jazer.htm