D.C. observes April 16th as Emancipation Day. From Wikipedia:
On that day in 1862, President Abraham Lincoln signed the Compensated Emancipation Act for the release of certain persons held to service or labor in the District of Columbia. The Act freed about 3,100 enslaved persons in the District of Columbia nine months before President Lincoln issued his famous Emancipation Proclamation. The District of Columbia Compensated Emancipation Act represents the only example of compensation by the federal government to former owners of emancipated slaves.