"The window is quickly closing," IRS commissioner John Koskinen said in a statement. "We encourage students, part-time workers and others who haven't filed for 2010 to look into this before time runs out on April 15."
People who earn so little that they aren't required to file a tax return often miss out on big refunds. That's because refundable tax credits, like the Earned Income Tax Credit, are designed to help low-income filers.
The agency estimates that half of the unclaimed refunds total more than $571.
Taxpayers in Alaska, Connecticut, Illinois, New Jersey, New York, Washington, West Virginia and Wyoming are missing out on the most money -- with unclaimed refunds in those states topping a median of $620.