Gidon married a Pilegesh (second wife) from Shechem. Was she Jewish? She bore him a son Avimelech. He convinced the people of Shechem to agree that he should become king. Were the people of Shechem Jewish in this story?
It would seem so. First of all, Yosam, in his speech to the people of Shechem, speaks of his father having "fought on your behalf... and saved you from Midian" (9:17), which wouldn't really fit if they weren't Jewish (Gideon didn't fight on behalf of the Canaanites or whoever, after all). Also, when Gaal ben Eved shows up (9:26), Rashi there says that "he was from a different nation," implying that all the protagonists up to that point were from the same (Jewish) nation.