It was first proposed four days after King's 1968 assassination outside a Memphis motel. It took 15 years until it became a federal holiday.

National Guard troops in Washington, D.C., patrol the Martin Luther King Jr. Memorial on Jan. 18, 2021. The memorial was closed to the public through Jan. 21 due to security concerns surrounding the presidential inauguration scheduled for Jan.

Though the holiday is young, this will only be the 25th year that all 50 states recognize it together. Here's what's open and closed on Martin Luther King Jr. Day.