If the bank account information on your tax return is not a valid account, the IRS will mail you a check, as DoninGA said. If it's a valid account, but not your account, your refund might be deposited in someone else's bank account. (Some banks check the name on the deposit against the name on the account, but not all banks check.) If your refund has not been issued yet, you might be able to stop the direct deposit and have a check mailed. See the following page on the IRS web site for more information.
What should I do if I entered an incorrect routing or account number for direct deposit of my refund...
