National Kindergarten Day was April 21, which was the birthday (in 1782) of Friedrich Wilhelm August Frobel, credited with establishing the first kindergarten—in 1837 in Germany.
In 2017, the U.S. Census Bureau says, an estimated 4,001,570 children were attending kindergarten in the United States.
More than 13 percent of those students were in California. It had the most kindergarten students—526,390.
Here are the 10 states that had the most kindergarten students in 2017.