1. Arizona was admitted to the Union on January 21, 1912: Arizona became the 48th state in the United States on January 21, 1912. Prior to achieving statehood, Arizona was a territory of the United States since 1863.

2. First-ever Arizona Governor inaugurated on January 21, 1912: On the same day Arizona was admitted to the Union, George W. P. Hunt was inaugurated as the first-ever governor of the state.

3. Martin Luther King Jr.'s birthday: January 21 is also the birthday of civil rights leader Martin Luther King Jr. Every year, the day is observed as a holiday in honor of King's work and legacy.

4. The 2000 Phoenix Open Golf Tournament ends in a four-way tie: On January 21, 2000, the Phoenix Open Golf Tournament ended in a four-way tie between Duffy Waldorf, Tom Lehman, Jose Coceres, and Chris Smith.

5. Arizona Coyotes franchise established: On January 21, 2015, the Arizona Coyotes announced that they had signed an agreement to form a new partnership with a group of local investors. The new ownership group helped solidify the future of the NHL franchise in Arizona.