1. On December 21, 1910, the first public library in the state of Arizona opened its doors in Tucson. The Carnegie Library, as it was called, was built with funding from the Andrew Carnegie Foundation.

2. In 1964, the Arizona State Board of Regents announced plans to establish a new campus of Arizona State University in Tempe. The campus, which eventually became known as ASU's Tempe campus, first opened its doors to students on December 21, 1965.

3. On December 21, 1994, the U.S. Environmental Protection Agency declared Tucson, Arizona to be in "serious" violation of carbon monoxide air quality standards. This designation led to new regulations and efforts to reduce emissions in the city.

4. In 1879, Arizona Governor John C. Frémont signed a bill authorizing the creation of Yavapai County, which covered a large portion of central and northern Arizona. The county was named after the Yavapai Native American tribe, and its first county seat was the town of Prescott.

5. December 21, 1946 marked the debut of the Arizona Republic newspaper's annual Fiesta of Lights parade in Phoenix. The parade, which still takes place today, features illuminated floats and marching bands and is held in downtown Phoenix to celebrate the holiday season.