It may be puzzling that a town, Jabesh-gilead, was being singled out for punishment, since the type of representation at the assembly was tribal (Judges 21:8), and regional (such as Gilead); see Judges 20:1–2. Towns and cities seemed to have featured only later, after the assembly, at the stage of recruiting fighters (Judges 20:14, Judges 20:17).
This is indeed a bit puzzling, but perhaps it points to Israel’s greater concern with finding a justified target than with being completely precise in how they found their target. The fact remains that the narrative’s concern is that upon investigation, it was discovered that no one from Jabesh-gilead had come to the assembly. That was taken to imply their tacit support for Gibeah and the Benjamites.1
8 And they said, “What one is there of the tribes of Israel that did not come up to the LORD to Mizpah?” And behold, no one had come to the camp from Jabesh-gilead, to the assembly.