1. On September 22, 1887, the city of Walla Walla was named the seat of Walla Walla County, after a heated political contest with rival city Dayton.

2. In 1915, the state's first automobile license plate law went into effect on September 22. The white letters on a dark background were required to be displayed on the rear of a vehicle.

3. September 22, 1973 saw the opening of the Seattle Seahawks' first-ever regular season NFL game, played at the Kingdome against the St. Louis Cardinals. The team lost 17-10.

4. In 2015, the US Forest Service and the National Park Service staff conducted a controlled burn of 700 acres on Mount Rainier, beginning on September 22. The burn was carried out to reduce the risk of future major wildfires and improve the health of the forests in the area.

5. On September 22, 2020, the Washington State Supreme Court ruled that the state's felony drug possession law was unconstitutional. The decision came in the case of State v. Blake, and resulted in the immediate release of hundreds of prisoners who had been convicted under the law.