It is not illegal if the account is still jointly owned. The fact that your marriage ended did not affect the ownership of the account or your rights to access it.
Before you think about taking funds from the account, make very sure you verify the account's status. Don't just assume that just because your name is still printed on any checks you get from your ex-husband, you are still an account owner. Check it out with the bank first. Your attorney can tell you whether taking money from the account will violate or affect your divorce agreement.
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