Emancipation Day in DC
Tax Day is traditionally April 15. So, why is it April 18 this year? You can thank Emancipation Day for your three-day reprieve. Here's why:

The standard: If April 15 falls on the weekend, the tax deadline is moved to Monday.

This year: Emancipation Day, April 16, is a legal holiday only in Washington, D.C.  Since it falls on a Saturday this year, it will be observed April 15. A federal statute says tax filings are impacted nationwide, so this year's tax deadline is Monday.

Next, let's get some background on Emancipation Day and how slavery ended in the U.S.
The Compensated Emancipation Act
On April 16, 1862, President Abraham Lincoln signed the Compensated Emancipation Act (read the document), which freed all slaves within the District of Columbia, the first in the nation to be freed by the federal government. The more famous Emancipation Proclamation took effect 36 weeks later, but the District of Columbia continues to celebrate Emancipation Day on the anniversary of the first act.

Proclamations notwithstanding, America's slaves weren't all freed at the same time.

Let's look at how slavery ended state by state.
Gradual emancipation
The following states passed their own gradual emancipation laws, designed to phase out the institution of slavery over a period of time.

Massachusetts
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Note: State constitution adopted with freedom clause, which courts interpreted as prohibiting slavery

Pennsylvania
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Rhode Island
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Connecticut
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New York
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New Jersey
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New Hampshire
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Granted statehood as a 'free' state
While in many cases slavery had already been abolished when they were territories, the following states were admitted into the Union as "free" states:

Vermont
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Ohio
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Indiana
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Illinois
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Maine
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Michigan
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Iowa
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Wisconsin
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California
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Minnesota
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Oregon
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Kansas
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Freed by the Emancipation Proclamation
Lincoln's Emancipation Proclamation of 1863 ended slavery in the following states that had seceded, provided the Union won the war:

Alabama
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Arkansas
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Florida
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Georgia
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Louisiana
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Mississippi
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North Carolina
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South Carolina
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Tennessee
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Texas
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Virginia
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