Jazer was part of a region overseen by king Sihon, an Amorite king that Moses and the Israelites defeated before they
crossed the Jordan River into Canaan.
The kingdom of Sihon used to be east of the Dead Sea. In the King James version, this town was called Jaazer in Numbers 21:32
and 32:35.
Before Joshua led the Israelites into Canaan, Moses granted the land from Sihon's kingdom mostly to the tribe of Gad.
Numbers 21:32:
32. After Moses had sent spies to Jazer, the Israelites captured its surrounding settlements and drove out the Amorites who were there.
Numbers 32:1-6, 34-36:
1. The Reubenites and Gadites, who had very large herds and flocks, saw that the lands of Jazer and Gilead were suitable for livestock.
2. So they came to Moses and Eleazar the priest and to the leaders of the community, and said,
3. "Ataroth, Dibon, Jazer, Nimrah, Heshbon, Elealeh, Sebam, Nebo and Beon--
4. the land the LORD subdued before the people of Israel--are suitable for livestock, and your servants have livestock.
5. If we have found favor in your eyes," they said, "let this land be given to your servants as our possession. Do not make us cross the Jordan."
6. Moses said to the Gadites and Reubenites, "Shall your countrymen go to war while you sit here?
...
34. The Gadites built up Dibon, Ataroth, Aroer,
35. Atroth Shophan, Jazer, Jogbehah,
36. Beth Nimrah and Beth Haran as fortified cities, and built pens for their flocks.
Joshua 13:24-27:
24. This is what Moses had given to the tribe of Gad, clan by clan:
25. The territory of Jazer, all the towns of Gilead and half the Ammonite country as far as Aroer, near Rabbah;
26. and from Heshbon to Ramath Mizpah and Betonim, and from Mahanaim to the territory of Debir;
27. and in the valley, Beth Haram, Beth Nimrah, Succoth and Zaphon with the rest of the realm of Sihon king of Heshbon (the east side of the Jordan, the territory up to the end of the Sea of Kinnereth).
Joshua provided towns for some of the Levites in 1 Chronicles 6:77-81 including Jazer: (also stated in Joshua 21:34-40)
77. The Merarites (the rest of the Levites) received the following: From the tribe of Zebulun they received Jokneam, Kartah, Rimmono and Tabor, together with their pasturelands;
78. from the tribe of Reuben across the Jordan east of Jericho they received Bezer in the desert, Jahzah,
79. Kedemoth and Mephaath, together with their pasturelands;
80. and from the tribe of Gad they received Ramoth in Gilead, Mahanaim,
81. Heshbon and Jazer, together with their pasturelands.
After Israel had begun to rebel against king David, David again counted his troops. During the count, they passed through Jazer in 2 Samuel 24:5.
1 Chronicles 26:31 denoted the support David received from those in Hebron who served in his military throughout the region:
31. As for the Hebronites, Jeriah was their chief according to the genealogical records of their families. In the fortieth year of David's reign a search was made in the records, and capable men among the Hebronites were found at Jazer in Gilead.
The 2 last occurrences of Jazer were prophetic mentions in Isaiah 16:8-9 and Jeremiah 48:32
