Two different variations of Ashtaroth exist in the Old Testament. First, it was a town associated with the kingdom of Og, king of Bashan.
Later, it appeared as a false god in the King James version of Judges.
According to a few different references in the book of Joshua, king Og "reigned in Ashtaroth and Edrei". Joshua 13:31 called them his "royal cities".
The first mention of Ashtaroth was in Deuteronomy 1:4:
3. In the fortieth year, on the first day of the eleventh month, Moses proclaimed to the Israelites all that the LORD had commanded him concerning them.
4. This was after he had defeated Sihon king of the Amorites, who reigned in Heshbon, and at Edrei had defeated Og king of Bashan, who reigned in Ashtaroth.
Moses and the Israelites had started taking lands an the area in today's southern Syria after the Exodus from Egypt. The 12 tribes of Israel divided the conquered land between them. After Moses died, Joshua continued the campaigns to acquire the land promised to Abraham's descendants. There was a brief reference to Ashtaroth in Joshua 9:10 when the Gibeonites tricked the Israelites into an alliance so they wouldn't be conquered like king Og of Bashan & the Amorite king Sihon of Heshbon.
Joshua 12:1-4:
1. These are the kings of the land whom the Israelites had defeated and whose territory they took over east of the Jordan, from the Arnon Gorge to Mount Hermon, including all the eastern side of the Arabah:
2. Sihon king of the Amorites, who reigned in Heshbon. He ruled from Aroer on the rim of the Arnon Gorge--from the middle of the gorge--to the Jabbok River, which is the border of the Ammonites. This included half of Gilead.
3. He also ruled over the eastern Arabah from the Sea of Kinnereth to the Sea of the Arabah (the Salt Sea), to Beth Jeshimoth, and then southward below the slopes of Pisgah.
4. And the territory of Og king of Bashan, one of the last of the Rephaites, who reigned in Ashtaroth and Edrei.
Joshua 13:8-12,29-31:
8. The other half of Manasseh, the Reubenites and the Gadites had received the inheritance that Moses had given them east of the Jordan, as he, the servant of the LORD, had assigned it to them.
9. It extended from Aroer on the rim of the Arnon Gorge, and from the town in the middle of the gorge, and included the whole plateau of Medeba as far as Dibon,
10. and all the towns of Sihon king of the Amorites, who ruled in Heshbon, out to the border of the Ammonites.
11. It also included Gilead, the territory of the people of Geshur and Maacah, all of Mount Hermon and all Bashan as far as Salecah--
12. that is, the whole kingdom of Og in Bashan, who had reigned in Ashtaroth and Edrei and had survived as one of the last of the Rephaites. Moses had defeated them and taken over their land.
...
29. This is what Moses had given to the half-tribe of Manasseh, that is, to half the family of the descendants of Manasseh, clan by clan:
30. The territory extending from Mahanaim and including all of Bashan, the entire realm of Og king of Bashan--all the settlements of Jair in Bashan, sixty towns,
31. half of Gilead, and Ashtaroth and Edrei (the royal cities of Og in Bashan). This was for the descendants of Makir son of Manasseh--for half of the sons of Makir, clan by clan.
In the King James translation, there were several mentions of a pagan god Ashtaroth that more than likely was a deity local to the region of Bashan in 1 Samuel chapter 7 verses 3-4, chapter 12 verse 10 and chapter 31 verse 10 and again in Judges 2:13 and 10:6.
Judges 10:5-6:
5. And the children of Israel did evil again in the sight of the LORD, and served Baalim, and Ashtaroth, and the gods of Syria, and the gods of Zidon, and the gods of Moab, and the gods of the children of Ammon, and the gods of the Philistines, and forsook the LORD, and served not him.
6. And the anger of the LORD was hot against Israel, and he sold them into the hands of the Philistines, and into the hands of the children of Ammon.