The IRS says 3,700 Montana residents who haven't filed their 2005 tax returns are missing out on a total of $3.1 million in refunds. Officials estimate that half the unclaimed refunds in Montana would be for more than $500. Taxpayers have a three-year window to file a return and claim a refund. The 2005 returns must be filed with the IRS by April 15, or the money goes to the U.S. Treasury. There is no penalty assessed by the IRS for filing a late return that qualifies for a refund. Taxpayers must also have filed returns for 2006 and 2007 to receive refunds from 2005. Nationally, more than a million taxpayers haven't filed 2005 tax returns and $1.3 billion in tax refunds have gone unclaimed. ___ Information from: KBZK-TV, http:// www.kbzk.com.