When was the first year all 50 states officially observed Martin Luther King Day?
USA Today - "On Nov. 2, 1983, President Ronald Reagan signed into law HR3706, the King holiday bill written and introduced by the late Rep. Katie Hall (D-Ind.) . Beginning in 1986, Martin Luther King Day — the first federal holiday honoring an African American — would be observed on the third Monday in January. King's birthday is Jan. 15.
Since that bill signing 35 years ago, the King holiday has evolved. In 1994, President Bill Clinton signed a law designating it a National Day of Service. By 2000, all 50 states recognized it as well. South Carolina and New Hampshire were the last holdouts."