This year (2011), the April 15th income tax filing deadline will not fall on April 15th. Rather, because April 16th is a legal holiday in the District of Columbia, it will periodically have nationwide income tax filing consequences. This year, Emancipation Day pushes the individual income tax filing deadline to Monday April 18th. See IRS Notice 2011-17 here.
What is Emancipation Day? Every holiday has a reason behind it, however, too often we simply take pleasure in the fact that the existence of the holiday somehow positively affects us without thinking about the reason for the holiday. Emancipation Day celebrates the day in 1862 on which President Abraham Lincoln signed the Compensated Emancipation Act to free over 3,000 slaves in the District of Columbia.
Back to the tax impact: Because in 2011 the holiday falls on a Saturday, it is formally observed on the preceding Friday. The preceding Friday is April 15th. When April 15th falls on a holiday, the next day that is not a weekend or holiday becomes the individual income tax filing due date. In 2011, this is Monday April 18th. As a result, all procrastinators will have that last weekend to take care of filing their returns.
You can find out more about Emancipation Day at the following links:
But the coolest link is here with images of the original act and transcriptions thereof: http://www.archives.gov/exhibits/featured_documents/dc_emancipation_act/