Did you forget to file your 2007 taxes? The IRS might have a nice check waiting for you.

Nearly 1.1 million taxpayers failed to file that year, and the IRS estimates they are entitled to $1.1 billion in potential refunds.

Half of those who failed to file are owed $640 or more, the agency announced Tuesday. And the median potential 2007 refund for people living in Wyoming was a high $788, while New Hampshire residents are owed a median refund of $741.

“Some people may not have filed because they had too little income to require filing a tax return even though they had taxes withheld from their wages or made quarterly estimated payments,” the IRS said.

But if you don’t file your 2007 return by April 18, 2011, say goodbye to your refund. Taxpayers have only three years to claim refunds before the money gpes to the U.S. Treasury.

If you do claim your 2007 refund, your check will be held until the IRS has received your 2008 and 2009 tax returns as well and any refund will be applied to  federal debts, child support or back taxes , the refund will applied to those amounts.