My cousin is single, but he filled out married on his W4. When he got his W2, it says he is married and is claiming 2 exemptions. Can he still file as single?

Yes, but he may find that he ends up owing money or gets a much smaller refund, since filing Married on the w4 means they take out less taxes.

Thanks Lisa 🙂

The W-4 you give an employer does not go to the IRS nor does it dictate how you have to file your tax return.  It just tells the employer how much tax to withhold from your paycheck. If he is single then that is how he should file.  He may have had too little withheld, and could end up owing tax.