Were the Mormons driven out of Illinois?

In a way, yes. The locals disliked the Mormons and attacked them several times, including murdering their prophet, Joseph Smith. The Mormons often retaliated. In order to preserve the public peace, the government asked the Mormons to leave Illinois and the United States within a year, and the Mormons cooperated.

The Mormons were previously driven out of Missouri by an extermination order issued by the governor.