$1.1 billion in unclaimed 2007 tax refunds

NEW YORK (CNNMoney) -- 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 a refund $640 or more, the agency announced Tuesday. And it could be even more: 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 Uncle Sam isn't holding your money for you much longer.

If you don't file your 2007 return by April 18, 2011, say goodbye to your refund forever. Taxpayers are only given a three-year window to claim refunds. After that, your money is scooped up by the U.S. Treasury.

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

In addition to a refund, some Americans may also be missing out on the Earned Income Tax Credit, which helps many low- and middle-income taxpayers.