When Gov. Tom Wolf puts pen to paper later today, Pennsylvania will become the latest state to officially recognize Juneteenth, which commemorates the end of slavery in the United States.

Pennsylvania will join 45 other states and the District of Columbia in either marking the day as a state holiday or observance. That leaves just four states that don’t recognize the holiday: Hawaii, North Dakota, South Dakota and Montana.

What is Juneteenth?

Juneteenth — a blending of the words June and nineteenth — is the oldest known US celebration of the end of slavery. It commemorates June 19, 1865. That’s the day that Union Maj. Gen. Gordon Granger rode into Galveston, Texas, and told slaves of their emancipation from slavery.

“In accordance with a proclamation from the Executive of the United States, all slaves are free,” Granger read to the crowd that day. It came more than two years after President Abraham Lincoln issued the Emancipation Proclamation.

African-Americans and others mark Juneteenth — also called Emancipation Day — much like the Fourth of July, with parties, picnics and gatherings with family and friends.

In 1980, Texas was the first state to make Juneteenth a state holiday, although it had been celebrated informally since 1865.

Is there a national holiday?

No, not yet.

The US Senate passed a resolution last year recognizing “Juneteenth Independence Day” as a national holiday, but it has not yet been approved in the House. The National Juneteenth Observance Foundation, an organization based in Mississippi, has worked for years to get Juneteenth recognized or observed as a national holiday for years.

In addition to working for national and state holiday observances, the foundation works with states to help create curricula for schools that will teach students about the history of black people in America from slavery to freedom.