“In the fifteenth year of King Amaziah son of King Joash of Judah, King Jeroboam son of King Joash of Israel began to reign in Samaria. He reigned forty-one years. He did what was evil in the sight of Yahweh. He did not depart from all the sins of King Jeroboam son of Nebat, which he caused Israel to sin.”
Now back to Israel, where King Jeroboam II ruled for 41 years. This was a long time and gets us to the mid 8th century BCE. He was the son of King Joash of Israel, just like King Amaziah was the son of King Joash of Judah. Of course he had the same name as the first king of Israel so he gets to be number II. He, however, like all the northern Israelite kings did evil in the sight of Yahweh, since he followed and sinned in the ways of his namesake and caused Israel to sin.