When did Martin Luther King, Jr. Day become a holiday?

The chronology of this holiday is actually quite complicated.
Dr. King was assassinated in Atlanta April 8, 1968. It wasn't until five years, in 1973, later that the first state signed a law making Dr. King's birthday a holiday. That state was Illinois, and the bill was sponsored by then assemblyman Harold Washington.
A bill was introduced in congress in 1968, after Dr. King's death to have his birthday observed as a national holiday. However, it wasn't until November 3, 1983 that President Reagan signed a bill establishing Martin Luther King, Jr. Day as a national holiday, taking place the third Monday of each January, with observance to officially begin January 20, 1986.
In 1986, the first time Martin Luther King, Jr. Day was observed as a national holiday, only 17 states had passed bills officially observing the holiday. By 1989, the number of states observing the holiday had grown to 44. In 1999, New Hampshire, the last state signed legislation making Martin Luther King, Jr. Day a state holiday.
In many communities, Martin Luther King, Jr. Day is becoming a day of service and reflection for the community.