BobKamman
Level 15

They don't make that easy to find with a Google search.  

2016 unclaimed refunds – deadline extended to July 15

For 2016 tax returns, the normal April 15 deadline to claim a refund has also been extended to July 15, 2020. The law provides a three-year window of opportunity to claim a refund.  If taxpayers do not file a return within three years, the money becomes property of the U.S. Treasury. The law requires taxpayers to properly address, mail and ensure the tax return is postmarked by the July 15, 2020, date.