Since the bonus was received via income earned during the course of the marriage, the answer is it's most likely still marital property. However, I would still need some specific facts specific to this situation to inclusively answer this question and give you a most accurate answer. And real life scenarios like this also hinge on multiple facts such as whether he's co-mingled it, has contributed, if there's interest, if he's kept it entirely separate, or anything like that. So, you're better off speaking with your lawyer and discussing the separate facts pertaining to your case with your lawyer.
Sean Sullivan is a family lawyer practicing in the Elmhurst, Illinois area at the law offices of Laura M Urbik Kern, specializing in child custody and dissolution in divorce. Visit his website, www.laurakern.com, and Divorce Magazine profile.